Most of us in central Lancashire have learned and sailed at Clowbridge. (RVSC)check the website http://ccgi.rvsconline.plus.com/htdocs/
I think theyre doin something for the national windsurfing weekend end of april...
theres also a review in the venues section. Old tom used to sort lessons but he's retired so i dont know what the current situation is.
I also had a few starter sessions at hollingworth res near rochdale, they have a centre.
You can also go on Fairhaven boating lake at lytham if you have kit. its only waist deep. when you progress just pop onto granny's bay next door

Enjoy