First, make friends with your local RNLI http://www.rnli.org.uk branch. They might have specific suggestions on places local to you that provide lessons, etc. They also will be the ones who come to fetch you when things go pear shaped, so you may as well know their names. :)

More to the point, find out if there are any local clubs that do regular races for small sailboats. Often they can give you a directory of people who are looking for crews for races. In my area I know boat owners would ask you to commit to a season of races, but some have told me I could come out for one or two races, just to see what I think. 
Crewing on someone else's boat is a great way to get started.  It will also let you find out if you really enjoy it or not.  
As a crewmember, you will have a boat full of mentors who will help you learn to sail. They will also be able to provide you with first hand knowledge of where to find a boat that is right for you when it comes time for you to buy your own.

Here are some random links to nudge you along in the right direction:
South Yorkshire Sailing Club http://www.sysc.org.uk/
Sheffield Viking Sailing Club http://www.sheffieldviking.org.uk/
Ripon Sailing Club http://www.ripon-sc.org.uk/
Scarborough Yacht Club http://www.syc.org.uk/

"Crew Wanted & Available" : http://www.ukdinghyracing.com/wantcrew.htm

If you actually need a specific club recommendation, I can perhaps inquire with people I know who know people. So to speak.

Before all that, if you want to play around a bit this Sailing Simulator has been recommended to me by several sailors:
http://www.nationalgeographic.com/volvooceanrace/interactives/sailing/index.html

Here are a few links that might help.

In my experience, it's best to master the small boats first. You get a lot more feel for interaction of the mainsail, the jib, and the rudder. You can spend more time watching the wind and the water. Larger boats are easier in a lot of ways, but that makes it harder to learn the feel of things.