Matching seperate first name and surname columns to an id no

I really need your help. I'm sure it's an easy one for you techie people. I am trying to find the membership number in a spreadsheet. I have searched using vlookup to find it using email numbers first:

=VLOOKUP(E1,'Member list'!A3:Z426759,2,FALSE)

However, I don't know how to do it with 2 separate columns. I though it might be as simple as putting the two columns together:

=VLOOKUP(C1&D1,'Member list'!A2:Z426759,2,FALSE)

Obviously that did not work either. I'd be really grateful if anyone could help me.

Thanks Lisa