Being in the East Midlands/Derbyshire area you are lucky in so much as there are LOADS of clubs in your area, your have all the East Midlands Clubs and as you are you are also near the Cheshire & North Wales Centre Clubs, who have clubs that run trials around the Macclesfield, Winsford, Congleton & Buxton area.
As previous posts mentioned you are probably best starting off with a "Dead Easy" type event just to get going again, no point tackling anything too daunting when you start out. Remember though, not all trials that advertise having an "easy" route are Easy Trials!!
Any trial specifically aimed at newcomers, people returning to the sport, or those who are just after a good days sport without busting a blood-vessel would be ideal. Usually they will have some mention to "Dead Easy" "Wobblers" etc in the regs.
Manchester17 are running a "Dead Easy" trial this Sunday at Victory Quarry near Buxton, so not too far away, and they can help you get your ACU forms sorted etc etc.
Website
Obviously this website & forum is a great place to find out information on forthcoming trials etc and more & more clubs have their own websites with trials calendars on etc.