Is just the salary I draw (to my personal UK bank account) from the German Ltd company or does it need to be the money the German Ltd company takes for my services (paid into the companies German bank account)?
i.e. Can the OR demand to see the German Ltd company accounts?
You need to advise the OR in your change of financial circumstances :-
income and new expenditure.
Provided that you are not the owner of the Ltd company then it is just your personal income that the OR is interested. If you own the company then the OR will be interested in the turnover and residual monies left in the company after your drawings