What they say about British weather is true!
While in England and Scotland the weather was fairly cool, it rained on and off, though rarely hard. We didn't see much sun (but were excited when we did). And you could get several diffferent types of weather in one day.
I will say that overall the weather was pretty good, as in - better then I expected (cold and rainy every day). The weather was cool, at times cold, but more often on the warmer side - you know - fall weather. There was quite a bit of wind, but that only affected me when I went to Hadrians Wall. The rain we did have was usually pretty light, the type where if you don't have an umbrella and are outside for a while you'll get wet, but not enough to necessarily open an umbrella if you had one. The only place where I felt like the rain impacted the group was when we took a cruise of Loch Ness, I think even Nessie hid from the rain.
The weather in the Fall makes England a little less hospitable, though I wouldn't forgoe a trip because it would be in the fall and the weather might not be great. I did miss the summer crowds and that can be worse then a chilly, drizzly day. But do bring a rain coat and some warmer clothes.