April in London, United Kingdom, brings average daily highs of 14°C and overnight lows of 6°C in the 2016–2025 historical record. Bring layers that work for a longer spell outside as well as a short walk. A warm extra layer gives you options when the day's weather feels cooler than the monthly average suggests.
In the record, at least 1 mm of rain or snow falls on 10 of 30 days on average, a daily chance of 32%. Leave some freedom to swap an outdoor day with a sheltered one. There is no need to read the average as a fixed number of lost days; it says nothing about how long rain lasts on each occasion.
The calculated day length, sunrise to sunset, averages about 14 hours. Sunshine averages 10 hours a day. The longer daylight window gives you more choice about when to be outside; it does not mean every part of the day will be sunny. Sunshine is a separate measure, and those hours need not arrive in one uninterrupted stretch.
For a culture-focused visit, group the places you want to see into manageable areas, with time between stops. Check each venue's opening dates before fixing the order. If food is a reason for the trip, leave time around meals rather than filling every gap with another journey. Check the places you choose for current opening hours.
May has an average daily high of 18°C, 4°C higher than April. Its historical rain-day chance is 31%, compared with 32% this month. If your dates are flexible, compare those trade-offs with the kind of days you want. Neither set of averages predicts the conditions of one particular holiday.