A London summer gives you light until after 21:00, an average July high of 23.9°C, and an Underground on which seven of the eleven Tube lines have no air conditioning. The city is built for cool weather and improvises in hot weather, so the trick is to use the evening, stay out of the deep Tube in the afternoon, and know where the water is.
The month-by-month events calendar sits in our guides to London in July and London in August, and the seasonal comparison is in the best time to visit London. This page is about how to spend a hot week here without wasting it.
Two facts shape everything. London is much further north than its summer temperatures suggest, which is why the evenings are so long. And almost no British housing, and only some of the transport, was designed to be cooled, which is why 30°C here is harder work than 35°C in a city that expects it.
London summer in numbers
- Average daily high
- June 21.6°C, July 23.9°C, August 23.4°C
- Average overnight low
- June 12.0°C, July 14.2°C, August 14.1°C
- Sunshine
- About 208 hours in June, 218 in July, 202 in August
- Rainfall
- 47mm in June, 46mm in July, 53mm in August
- Wet days
- Roughly 8 a month with 1mm or more
- Longest day 2027
- Monday 21 June, solstice at 14:11 BST
- Daylight then
- About 16 hours 39 minutes
These are Met Office 1991-2020 averages for the Heathrow station. Central London sits a degree or two above them at night, because the built-up area holds heat.
The long evening is the whole point
The Royal Observatory puts the 2027 summer solstice at 14:11 on Monday 21 June, and the longest day in London runs 8 hours 49 minutes longer than the shortest. From late May to mid-July there is usable light until well after 21:00.
That is more useful than the temperature. It means a full working day of sightseeing followed by a second, calmer evening: a park at 19:00 with the heat gone out of the day, a river walk at 20:00, a beer garden at 21:00 still in daylight. Restaurants that are impossible at 19:30 have tables at 21:00 and the sky is still light.
The corollary is that mornings are wasted. Nothing much opens before 10:00, and the first two hours of a summer day are the coolest and the emptiest. Use them for whatever involves queuing.
Book the big paid attraction for opening time and the park for the evening. Queues at the Tower of London, the London Eye and the South Kensington museums are at their worst between 11:00 and 15:00 in July and August, which is also the hottest part of the day. Doing the ticketed thing first and the outdoor thing after 18:00 halves both the waiting and the sweating.
What "no air conditioning" actually means
The distinction is between the sub-surface railway and the deep tube tunnels. Transport for London's fleet of 192 air-conditioned S-stock trains covers the Circle, District, Hammersmith & City and Metropolitan lines, which together make up about 40 per cent of the Underground. Elizabeth line trains are air-conditioned too, and the DLR and the newer Overground trains are climate-controlled.
Everything else is not. The Bakerloo, Central, Jubilee, Northern, Piccadilly, Victoria and Waterloo & City lines run in narrow deep tunnels with nowhere for heat to go, and the trains have forced ventilation rather than cooling. On a hot afternoon a Central line carriage is the least pleasant place in London.
Above ground there is more choice than people realise. Buses are ventilated and you can see out; the river is cooler by several degrees; and walking in the shade of the parks beats any of it. Our guide to avoiding rush hour applies double in a heatwave, because the crush and the heat compound each other.
| Getting around on a hot day | Comfort |
|---|---|
| Elizabeth line | Air-conditioned, fast, deep but cool |
| Circle, District, Hammersmith & City, Metropolitan | Air-conditioned S-stock |
| Deep-level Tube lines | Ventilated only; avoid 15:00-19:00 |
| Bus | Windows and shade on the lower deck; the top deck bakes |
| River bus | The coolest way to cross central London |
| Walking | Fine in the parks, hard on the pavements |
When a heatwave is declared
The UK Health Security Agency runs a Heat-Health Alert service with the Met Office from June to September. Alerts are colour-coded yellow, amber and red, and they are based on the likely health impact rather than on a single temperature. A yellow alert affects vulnerable people; amber means impacts expected across the whole health service and the whole population at some risk.
Transport for London's own advice on hot days is unglamorous and correct: check your journey before you set out, carry water with you, give up your seat to anyone who needs it, and speak to a member of staff if you feel unwell. Do not get on a deep-level train if you already feel faint, and do get off if you feel worse; staff would far rather deal with you on a platform.
Drinking water is free and easy to find. Licensed premises must supply free tap water on request, and there is a network of public refill points; our guide to tap water and refill points maps them. Carry a bottle, because buying one every two hours adds up quickly, as our breakdown of what a day in London costs shows.
British hotel rooms often have no cooling, and nobody tells you before you book. Air conditioning is standard in modern chain hotels and in the upper end of the market, and absent from a great many Victorian conversions, guesthouses and budget rooms. In July and August it is worth filtering for it explicitly, or at least asking whether the windows open and whether a fan is available. A top-floor room under a roof in a heatwave is a bad night.
Where to swim
Outdoor swimming is the thing London does unexpectedly well, and in summer it is cheap.
- Serpentine Lido, in Hyde Park, usually runs from June to mid-September, with weekend sessions from mid-May. An adult full day is £8.40, a session £6.50, and after 16:00 it drops to £2.50. Under-16s must be with an adult. See Hyde Park and Kensington Gardens.
- Parliament Hill Lido on Hampstead Heath is a 60-metre unheated pool. In the summer season a morning or afternoon session costs £8.80 for an adult and £2.70 for a child aged 5 to 15, while the 07:00 breakfast swim is £5.00 and free for children. Evening sessions are adult lane swimming and do not run on Tuesdays, Saturdays or Sundays.
- The Hampstead bathing ponds cost £5.00 all year, with three separate ponds. Summer sessions are partly bookable and sell out in hot weather; drop-in slots run in the mornings.
Book the bookable sessions the moment a heatwave is forecast, because that is exactly when everybody else does. Our guide to London's swimming ponds and lidos covers the rest of the city, including the lidos south of the river.
Parks, roofs and the river
London has more usable green space than almost any comparable city, and in summer the parks stop being scenery and become the venue. Deckchairs are hired in the royal parks; most other parks are free to sit in. Evening concerts run in several of them through July and August, as our guide to summer concerts in the parks explains.
The river is the other cool corridor. Uber Boat by Thames Clippers runs a scheduled river bus with open rear decks, and it is the most comfortable way to cross central London on a hot afternoon; fares and zones are in our guide to the Thames river bus. Riverside pubs get the breeze, and our guide to riverside pubs on the Thames picks the ones worth the journey.
Rooftops are the summer cliché and some of them are free: see roof gardens and free terraces. Beer gardens fill from about 17:00 and there is no table service, so send someone to the bar early; the rules are in our guide to beer gardens in London.
The things that only happen in summer
Some of London is closed for ten months of the year. The State Rooms at Buckingham Palace open for a summer season only, which in 2026 ran from 9 July to 27 September; outside it, access is limited to small guided tours on selected dates. Our guide to Buckingham Palace explains the tickets.
Open-air theatre, outdoor cinema, the lido evening sessions, the swimming pond bookable slots and most of the big park events are summer-only too. So is the Olympic Park at its best: the fountains, the waterways and the playgrounds are designed for warm weather, as our guide to the Queen Elizabeth Olympic Park describes.
Against that, this is peak season. English school holidays run from roughly the third week of July to the end of August, and that is when families from everywhere else arrive too; our guide to London in the school holidays sets out the dates. Late June and the first half of July are the sweet spot: full daylight, warm weather, term still running.
A hot day that works
Start at 09:00 with the ticketed thing, or with a market before it fills. Move indoors to a museum or a gallery for the middle of the day, because they are large, stone-built and much cooler than the street. Eat late lunch indoors.
Get on the water or into a park for the late afternoon, and swim if there is a lido within reach. Eat dinner at 20:00 outside. Walk a bridge at 21:00 while the sky is still light. Take a bus rather than a deep-level Tube home.
Done that way, a hot London day is one of the better things this city offers. Done the other way round, standing on a Central line platform at 16:30 in August, it is not. The winter version of the same argument is in our guide to London in winter.
Frequently asked questions
How hot does London get in summer?
The Met Office 1991-2020 averages for the Heathrow station give an average daily high of 23.9°C in July and 23.4°C in August, with overnight lows around 14°C. Individual heatwaves go considerably higher, and the UK Health Security Agency issues colour-coded Heat-Health Alerts with the Met Office between June and September.
Does the London Underground have air conditioning?
Partly. The Circle, District, Hammersmith & City and Metropolitan lines use 192 air-conditioned S-stock trains, covering about 40 per cent of the network, and Elizabeth line trains are air-conditioned. The deep-level tube lines, including the Central, Northern, Piccadilly and Victoria, are ventilated but not cooled.
How late does it stay light in London in summer?
Very late. Around the solstice in late June there are roughly 16 hours 39 minutes of daylight, so there is usable light well after 21:00. British Summer Time adds an hour to the clock from late March to late October, which pushes the whole evening later.
Where can I swim outdoors in London?
Serpentine Lido in Hyde Park usually opens from June to mid-September, with adult day tickets at £8.40 and a cheap late session after 16:00. Parliament Hill Lido on Hampstead Heath is open all year, and the Heath's three bathing ponds cost £5.00 for an adult. Several other lidos operate across south and east London.
When is the best time to visit London in summer?
Late June and the first half of July, before the English school holidays begin. You get close to the maximum daylight and warm weather without the peak-season crowds and prices that arrive from the third week of July. Book anything ticketed well ahead if you travel in August.
Sources
- Met Office - Long-term averages, Heathrow station, 1991-2020 (checked September 2026)
- Royal Observatory Greenwich - The summer solstice (checked September 2026)
- Met Office and UKHSA - Heat-Health Alert service (checked September 2026)
- Transport for London - Four Lines Modernisation (air-conditioned S-stock fleet) (checked September 2026)
- The Royal Parks - Swimming at the Serpentine Lido (checked September 2026)
- City of London Corporation - Hampstead Heath swimming opening times (checked September 2026)
- NHS - How to cope in hot weather (checked September 2026)
- Royal Collection Trust - Buckingham Palace summer opening (checked September 2026)