Generally in the UK the responsibility for the warranty is actually with the dealer.
just to help with a little bit of info. This is true, and whilst your warranty is with the dealer you bought the bike from - the dealer isn't forced to do the work, unless of course they want to. Most high end components, ie suspension etc have a technical support centres in the UK that does the work for dealers.
Some dealers are happy to strip a pair of forks and service them, some will pull apart a rear shock and service that. Some realise their time is better spent, so any part goes to the experts to be serviced / inspected & repaired under warranty.
The same is true for Bosch. Just as any competent home mechanic can fix this problem, any dealer should be able to do it. But just as you might not be happy doing it yourselves, the dealer might also like to have the experts, and those who are actually paid to do so... look at it.
hope that helps.
Col