can i open more than one account on my name with betfair?

yes

1. Mail them and say you wish to test some idea's, or keep backing/laying seperate, or whatever and need another account.
2. Mention you have heard some mmbers have master/sub accounts and wondered if you could have one as well
3. Hope for the best

Your main account will then become a 'master' a/c allowing you to set up 'sub' a/c's as you need them