Actually on a jumpseat agreement we don't have to pay taxes going to the UK, only returning. It is a bit different between a jumpseat agreement and a non-revenue agreement.

One of our non-revenue agreements is with British Airways. We get 1 free standby pass a year, that catch is we still have to pay taxes, international taxes. So last year I flew BOS-LHR-BOS on British Airways. The ticket was free but I still had to pay $225 in taxes. Not a bad deal concidering the cabin crew upgraded us to business class in both directions.

MaxJet, EOS, and Omni are the only carriers that allow us to jumpseat to European destinations.