I did a taster session at Lee Valley and really enjoyed it.I used to ride a fixed bike quite a lot, so that bit will be okay. Not used to no brakes though
Also, I assume no cleats - so is it clips/straps?
Their hire bikes come with Look cleats if i remember correctly. You can take your own shoes if you use Look cleats or they have shoes available for hire.
No idea whether that applies to Derby or not.