As suggested, the easiest option would be to speak to your dealer if it’s a new car, they should be able to help and arrange fitting before collection. They’ll almost certainly subcontract it to a third-party specialist.
If you’d prefer directly with the fitter then there are lots of tracker manufacturers and even more fitters to choose from. I would personally gravitate towards Smartrack (Global Telemetrics) and Tracker.
Ask for it to be fitted at the dealer before collection.
SmarTrack are leading suppliers of high quality vehicle tracking devices and systems throughout the UK for cars, motorcycles, fleets and more.
smartrack.uk.net
Tracker has over 25 years experience in the tracking and recovery of vehicles, and has built a working relationship with all UK police forces.
www.tracker.co.uk