I donīt think the lack of a stamp in the warranty book will be a problem, but you might want to go back to Evans Halshaw and see what they can do for you. Perhaps a call from them to Renaultīs warranty dept will sort that out for you - in any case, Renault should know when one of their cars was first sold/registered.
As for servicing, no you do not need to go to Renault to have it done. The rules on manufacturers warranties were changed a few years ago to stop manufacturers from forcing you to use their franchises - canīt remember the name they gave the new rules, but suffice it to say all you need to do now is make sure you use a VAT registered garage (someone please correct me if Iīm wrong on this!).
Bear in mind though that these days most cars need to be hooked up to a computer, and a small back street garage may not be able to afford the kit needed to do a proper job. Yes, they can do the
and filters etc but they may not be able to do a full diagnostic, nor reset things like the service warning light and so on.
For me, I wasnīt happy to pay Renaultīs fixed price servicing costs at their own dealers and their franchisees, so I opted to use a Renault Specialist who serviced my 55 Laguna with Renault oils and parts and according to Renaultīs service schedule. In fact they were formerly a Renault Main Dealer and I saved a packet, with my warranty intact. A quick search of this site will throw up a few independant specialists for you.