London in the Middle of April. The rise in temperatures is gradual and in mid-April,the thermometer climbs a notch making the atmosphere in the middle of the day rather pleasant. Temperature 11 °C 52 °F. London Weather April Averages, United Kingdom. Rainfall Days 16 days. Night Temperature 9.8 °C 50 °F. Back to top. Weather reports from April 2019 in London, England, United Kingdom with highs and lows Late night and early mornings tend to remain cool early in April, averaging near 4-5C (40F) with a few colder mornings dipping to near 32F (0C). Get the monthly weather forecast for London, London, United Kingdom, including daily high/low, historical averages, to help you plan ahead. Day Temperature 10 °C 50 °F. However, when the fog dissipates, which happens most of the time, the rest of the day is beautiful with a superb weather in London throughout April. Sunshine Hours 5 hours. Low Temperature 6 °C 43 °F. Towards the end of April, mornings will mostly be 7-8C (in the mid-40s F). High Temperature 13 °C 55 °F. Rainfall 43 mm.