Done this a couple of times, try the following:
Get an MOT on the bike using the frame number, not the registration number.
Arrange insurance using the frame number with the proviso that you provide the insurer with the new UK registration number as soon as it's issued.
Go to the local DVLA office, give them the MOT & the original documents from Germany. They will charge a few £££ for transferring the "nationality" of the bike. They may also fax the German documents to the German Embassy to ensure that the bike is not stolen (or subject to finance?). They charge £25.00 (?) for this.
They will tell you what your new registration number is. You will also have to buy Road Tax (6 months min) at this point (£33.00?).
Phone your Insurance company & tell them the reg. number.
Get a number plate made.
Logbook will arrive within a couple of weeks max.
To pass the MOT:
Leave the Speedo alone, cheaper option is buy a bike specific sticker that goes on the speedo face, giving equivalent mph figures.
On some bikes, a piece of black tape (insulating) in the correct place will allow it pass an MOT - this will stop the beam dazzling oncoming drivers. I assume you have an 1100GS - this should work as it did on an R80GS for me similar headlight.
Mind you, one benefit of delaying all of the above is that you can forget about Parking Tickets
