What is the weather like in London, England in September/October?
Unfortunately the thing with the British weather is that it can be unpredictable and one year is never the same as the next. September/October is the very end of summer/beginning of autumn so temperatures can fluctuate, but it won’t be very, very cold. It certainly shouldn’t be snowing. I’d say as a very rough guide expect temperatures to be between about 14 and 21 degrees Celsius. The best thing for you to do would be to bring layers with you, t-shirts in case it’s warm in the day and then some sort of sweater you can throw on in case it gets cold. It would probably be a good idea to bring a light jacket too as even if it is warm during the day the nights will be a little chilly by that point.
