Help with icloud with an existing @me.com account

Hi all

I already have an @me.com account, but on my iphone it will not let me set up icloud as my registered email account with apple is a btinternet.com one & it tells me I have to create a @me.com account

I have put in my existing one & rightly it tells me this is taken, but doesn't give me the option to use this only to create a new account

Anyone have any ideas??

Thanks

Phil