I have now booked my trip and have to say am very suprised with the solution.
I once again checked avios, nothing in business or economy. Then went to kayak / BA and LH sites and nothing suitable for less than £200 (economy). Started checking Cologne and DUS for flights and train times and more or less found something suitable. before booking, I thought I would try Miles and More….
EVERY SINGLE MORNING LH FLIGHT LON-FRA was open and available….. booked !
One question though, why do Avios charge £17 for the additional charges and LH/Miles and More charge £75 for the additional charges…?