Britain has a very temperate climate, rarely extremely cold and nearly never too hot, particularly in the north. It is often categorised, with some fairness, as rainy. However, on this rain depends the verdant green and the many bodies of fresh and running water that characterise the landscape.
Travel in Britain can be enjoyed year-round with some seasonal event or another to build a trip around. However, the warmest, driest months tend to be July through September. But there are no guarantees and even good weather can be changeable. Make sure to bring a coat and be rewarded. The wet brings a depth of atmosphere and when the sun does shine, there are few places more beautiful and refreshing.