Can anyone explain to me why I need to unplug my BT landline phone to get my Sky wireless broadband to work?

Most electricians will not be able to solve this problem! You need a telecoms enginner which is a separate trade in its own right. As the other poster has pointed out, its seems like its an ADSL filter issue. Could be a faulty filter, filter not fitted, etc.

Is this a recent problem or has it always been like this? If it has previously worked ok, have there been any recent changes - either with phone or broadband services? Have you tried calling Sky? I assume the BT line was there before the Sky BB was installed, and that it was working previously? Do you have ADSL micro-filters on every phone socket to which there is a phone connected? Do you have more than 4 phone devices (phones, fax machines, ADSL modems...) connected to the same phone line? If so, have you tried disconnecting any of them?

and how much do you think a qualified electrician would charge ,96 quid sounds good to me