I'm not an easyjet pilot so i can't comment in depth, and as far as i know they have by now german contracts, not english ones anymore.
German taxation rules change constantly and around 2 or 3 years ago they changed the taxation of workers, like pilots, that have a base in germany so that they are taxed in germany. As far as i know the result was that easyjet pilots had to pay taxes retroactively which amounted to quite a lot of money and a severe pay cut.
There was some discussion about the topic in here as well back then, try to find them or some easyjet pilots as i know some of them are active on pprune.