This depends. All warranties will require you to get your car serviced at a reputable garage at specified intervals. However, manufacturers’ warranties can’t tell you where to get your car serviced or make you get the service from one of their dealerships. You can go to an independent garage and the warranty will still be valid.
However, if you get an aftermarket warranty from a dealership, they can require you to get your car serviced at one of their garages in order for your warranty to be valid. Warranties from independent providers may have a list of approved garages where you can get a service from, or they may accept services from any VAT registered garage. Check your terms to see what your car warranty requires.