In the US we have the Magnuson-Moss Act which requires O.E.M.'s to hold valid warranty claims although service work had not been completed at the O.E.M.'s dealer network. As long as said work was done correctly and with correct parts etc.
The UK has a similar law, the European Block Exemption law.
Click here for an article about the EBE lawIn today's market place, it would very hard to believe that an O.E.M. could void a car's warranty because on non dealership service work.
In the old day here if you modified vehicle with non original parts, say customer exhaust, the O.E.M. would claim that if your alternator took a crap, that because you had modified your vehicle, your warranty was no longer valid. The Magnuson-Moss Act covers this sort of thing too.
I would do some research and not let the O.E.M. bully you into having all work done by the dealer. Just make sure that you keep records of the work. I service my own new Harley and as long as I use the approved grade/class of oil and a Harley filter, I'm good to go.
