This is where you find out about it all:
http://www.parkrun.org.uk/
For those who haven't heard of it, it's basically a group of people that meet up to run 5k as a fun, family event catering for all standards from beginner trying to get fit or loose weight to very quick club runners.
It's free to do it, very friendly and they do them all over the country on a Saturday morning at 9am. Very motivating, everyone gets cheered at the end and there's absolutely no pressure to do anything but run at your own pace and enjoy yourself.
The kids really love doing it too, I'd highly recommend it as a good way of getting a bit fitter for a relatively small effort.
I started running 5k last summer as a bit of fitness training for cycling, I was running and walking it having never run that far before and did my first one in 45 minutes, I did today's in 31 which is my 10th run so you can see how quickly you can improve. It took me two runs to run a whole 5k without stopping and I've been up to 10k so far. The last couple of runs I added 20-25 miles on the bike each time as training for a duathlon next month.
Pic on the way there this morning on the bike:
