EU tax laws are perfectly simple and understandable, even for pilots...
If you live and work in the EU then you must pay tax - somewhere in the EU. This may be in your country of residence, or country of employment. One or the other, not neither, not both.
If you are naive enough to imagine that by being paid in £ ex UK whilst working in Germany you can bamboozle the tax authorities that you work in Germany so don't need to pay UK tax, and then tell the Germans that you are a UK employee so don't have to pat German tax then you're stacking up a whole load of trouble. Upon your return home when the UK tax office asks you "where have you been for the last x years, and where have you been paying tax?" they will want receipts - proof - that tax was paid elsewhere. If you can't give that they'll typically send a bill for the tax outstanding (pretty grim if you've spent it over the last few years) and then add a punitive charge of often the same again. Else you can go to court, get a Criminal record (ID card implications) and get fined even more.
D'oh!