Well done!
I need to find a club down my way
Mate, if you're in South Bucks, Denham can't be too far away for you.
There is an informal* group that rides out from near the
nursery on the A40 opposite where Denham car boot is. I've been out with them a few times. They have 2 groups, amusingly known as the "medium" and "fast" groups (there is no "slow" group). I just turned up as a noob and they took me under their wing.
The "medium" group does about 30 miles, usually with a tea stop at Jenners in Maidenhead, and a pace of I guess 15-16mph ave. They do ride in formation, which takes a bit of getting used to, and they'll expect you to do so too, but they'll give you tips and are generally quite laid back.
My first time in the "fast" group was a bit of a shock. Having ridden with the "medium" group enough to get the hang of the bunched up riding and to get my fitness up, my mate Lee (who is a serious hardcore ex-racer) convinced me I should ride with his group. This group rides a LOT faster and probably do more like 45 miles without stopping, at more like a 19mph average. A lot of the fast group are racers but if you go during race season with a bit of luck they'll be "saving themselves for tomorrow" so slightly slower. I didn't get dropped, but it was hard work and someone actually rode behind me pushing my saddle to help at one point! That was a couple of years ago, so if I went back now I'd definitely go back to the "mediums".
Get yourself down there, I believe it's a 9am start on Saturdays.
* I say informal, because I heard about it from a mate and there didn't seem to be any sort of club strip or anything, just a couple of groups of 'regulars'.
A bit of internettery leads me to believe it might be the
Willesden Cycling Club