Protecting the deposit before it's actually received

I have a new tenant who is moving in on Saturday. Initially the plan was to meet up before the move in date to sign the AST and tenant was going to do bank transfer then move in few days later once money had cleared. They now want to pay with bankers draft on Saturday. I like to have all the paperwork on move in day including the deposit details so that I can get them to sign to say it's all been received etc. I know I could send it with recorded postage or return a few days later but I want to get everything done on Saturday if possible.

Are there any problems with protecting the deposit on the morning before its actually been received other than potentially losing my fee if for some reason the tenant doesn't actually move in.

I don't see how it could happen but potentially could the tenant claim back the deposit from the deposit scheme if they found out it was protected and they didn't actually move in, even if they hadn't actually paid a deposit. They would have no evidence of the actually tenancy etc.

Bit of a weird question I know but thanks in advance and I hope my question makes sense.