Spring, roughly late March to May
The consensus favourite, and deservedly so. The parks come back to life, the days lengthen quickly, and the city looks its best. Blossom season in the royal parks and the squares is genuinely lovely and genuinely brief.
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The catch is that peak bloom is unpredictable to within a couple of weeks, and building an expensive trip around it is a gamble that frequently loses. If flowers are the point, aim for a wide window rather than a specific weekend, and treat any particular display as a bonus. Easter also floats between late March and late April, dragging prices and crowds with it wherever it lands.
Rain is frequent but light, and the weather is genuinely changeable within a single day. Layers, not a forecast.
Summer, June to August
Long daylight, up to about sixteen hours in June, outdoor everything, festivals, and the warmest weather. It is also the most crowded and the most expensive, with school holidays from late July compounding both.
Two things visitors underestimate. The Underground gets genuinely uncomfortable in a heatwave, because much of it is deep, old and not air conditioned. And July and August are when many Londoners leave, so some of the best restaurants and smaller venues close for a fortnight.
Late August has the Notting Hill Carnival, which is spectacular and which reshapes west London traffic and transport for a weekend. Plan around it rather than into it if you are not going.
Autumn, September to early November
Arguably the best value in the calendar. September in particular keeps much of the summer's weather while the school holiday crowds have gone, and prices soften from the middle of the month. October brings the parks turning, the theatre season proper, and comfortable walking weather.
Daylight shortens quickly, though. The clocks go back in late October and by early November it is dark before five, which changes how much you can fit into a day. Half-term at the end of October produces a sharp one-week spike in family travel and airport congestion.
Winter, mid-November to February
The cheapest and the most misunderstood. London in winter is cold rather than freezing, wet rather than snowy, and dark by mid-afternoon. That is a genuine drawback and it is also why hotel rates fall and museums are pleasant rather than heaving.
Late November to Christmas is its own micro-season, with lights, markets and a distinctly busy, expensive fortnight around the holidays themselves. The gap between Christmas and New Year is chaotic. January and early February are the quietest and cheapest weeks of the year, and for a museum-and-restaurant trip they are a strong choice that almost nobody recommends.
The travel-day arithmetic changes by season too
This is the part seasonal guides miss. When you visit changes not just what you pay for a hotel but how your arrival day goes.
Summer and school holidays mean longer immigration queues, fuller flights and heavier road traffic to and from the airports. Half-term weeks concentrate family travel into a few days and airport drop-off zones behave accordingly. Winter brings the genuine disruption risk: fog and freezing conditions cause more delays and diversions at UK airports than snow ever does, and short daylight makes an unfamiliar late arrival harder.
The practical consequence is that the buffer you should build into a travel day is not constant. A February arrival deserves more slack than a September one, and a late-December departure deserves the most slack of all.
Cheapest: January and early February. Best value with good weather: September. Best weather: late May to early July. Longest days: June. Busiest and priciest: late July, August, and the fortnight before Christmas. Most disruption risk: December and January.
Should you build a trip around a specific event?
Only if the event is the trip. Anything weather-dependent, blossom, autumn colour, a clear day for a view, is a poor anchor for a booking made months ahead. Fixed-date events, a match, a show, a race, are different: they are reliable, but they also move hotel prices and clog transport for miles around, so book accommodation and your airport transfer early rather than assuming availability.
