- there are more and more G-regs operated in the EU outside the UK. What avionics- / pitot static- / altimeter- / transponder checks are required for privately operated G-regs
during the annual ( or biennual ) airworthiness review to keep them legal for IFR-flying?
Most G-regs operate on the LAMP system, which requires testing in accordance with CAA CAP 766 which is quite the same as testing in Germany, The Netherlands etc.
it is the same testing, but much cheaper around £120, whereas in Germany the test mafia wants €1200 for the same tests
There is no reason why a D-reg avionics test should be done in Germany if you don’t want that. You are free to perform this test in other countries as well. Same is true for most other countries.