OK
So you have now told us what your BMW branded Extended Warranty insurance policy says:
All service work must be carried out by an authorised BMW Bike dealer
Over to UKGSer's resident panel of experts as to:
(1) What the words mean
(2) Their legality or enforceability, with reference to Contract law and/ or EU directives and / or Consumer legislation and / or 'Bikers rights' and / or what they heard from their mate and / or that it's all a rip off as it won't pay anyway, so take it to Steptoe or do it yourself, mate.
(3) What to do next
Here's an abbreviated summary of the replies to date:
Timaloy tells us that he rang someone who said that the stipulation could be set aside, the only requirement was that the service(s) should be conducted in line with the manufacturer's schedule.
Ted doesn't seem so sure that the words can be set aside.
BBB666, believed the words you have given used to be used but had now been changed, to allow independent servicing, providing the service is conducted by a VAT registered entity.
1130CC seems to float somewhere between Timaloy, Ted, BBB666 and mentions a VAT provision, too. He goes on to suggest doing it yourself, which (if you are not VAT registered) might bring you into conflict with BBB666's understanding of the VAT requirement.
Sgt Bilco has set the entire provision aside, clearly pointing you in the direction of an independent service but without the VAT requirement.
So, some overlapping but sometimes conflicting advice, some more onerous than others. What now?
You can plump for the reply that suits you best. Of course if you never have to make an extended warranty claim you will never know if it was the right thing to have done, but it won't matter. If it does prove to be the wrong decision, no doubt UKGSer will be right behind you with support and / or alternative views.
You can await more advice from UKGSer.
You can contact the insurer of your policy and satisfy yourself.
You can contact BMW, the agent who sold you the insurance policy and satisfy yourself.
You can do whatever you think best.