Tesla vehicles are currently excluded from GAP insurance cover:

Unfortunately, we (GAPinsurance.co.uk) are no longer able to provide GAP insurance cover for Tesla vehicles (unless you're an existing customer of ours already, in which case it might be possible and you should contact us for further assistance).

We do however have a sister-brand: DriveWISE.co.uk which can currently faciliate GAP insurance cover for a Tesla.

See the links below for more details:

DriveWISE.co.uk logo

GAP insurance:
Private Vehicles

GAP insurance:
Driving Instructors

GAP insurance:
Taxi Drivers