Tax query (Alicante)

I have just started a p/t job in Alicante and have registered with an NIE & S/S number, however when I went to the bank to setup an account I was told I have to pay UK tax on my Spanish salary until I become resident? Yet my boss says because I live & work here and have a Spanish contract I should be paying Spanish tax? So now i'm worried I'm going to get taxed twice! Can anyone advise which is correct?