A further update - we called Tesla at the Gatwick branch, and they gave us two companies that do body/paintwork for Tesla cars. One was Apollo (in Horsham) and the other was Finesse (in Dorking). Apollo quote £1000 based on the photo we sent them. Their labour alone was close to £800. Seemed a little steep! Finesse wanted us to bring in the vehicle so they could look at it first hand.
We took the car to them this morning, bright and early for an assessment and judging by their yard (full of BMW, Audi, Tesla, Mercedes, Mini, first impressions were it will be expensive), but after the friendly gentleman inspected the tear and explained what they would do and said, £450 with a courtesy car thrown in for a couple of days, I felt a lot better. I asked them how they would blend the colour and he explained how so hey! what do I know? Fortunately where that gash is low down and it's quite a small area they would have to match up. He said we shouldn't worry about anything because they had Tesla qualified staff.
Everything from that point onwards was handled very professionally and efficiently, even the young lady inspecting the car, putting it into Service mode (which I didn't even know we had) and the friendly staff inside, so far so good.
Driving home in the 2021 Vauxhall courtesy car, I really did miss the one pedal driving and regen braking. As for that terrible petrol engine noise on acceleration, and the horrible dash with all the buttons, it is quite incredible how distracting all the knobs and buttons can be.