Fees for drawing up/checking/allowing you to sign the tenancy agreement are illegal.
Only in Scotland - not in England where letting agents can charge a fee for pretty much anything so long as they are being transparent. The only things they are unable to charge for are for registering with them or for giving you a list or properties (there may be one other thing but I can't remember!).
That said, I'm assuming you have not seen the TA as yet. This should set alarm bells ringing. Somewhat inscrupulous agents tend to present the TA for signature on the day tenants are due to move in - only then do the tenants become aware of the nasty clauses included, such as 6 monthly above inflation rent rises. It is then too late for them to pull out.
I would strongly recommend walking away. Without knowing what you have signed it is difficult to know the extent to which you are contractually tied but, if it was merely a credit check agreement, then you have no further obligations.