This appears to be a genuine TWR enhanced XJ-S, with full body kit, wheels, badging, trim and mechanical enhancements from TWR. This example was asking $49,990 (AUD) on Ebay Australia in October 2017, and the seller made the following comments at the time of offering:

This particular example was first registered to Ron Hodgson and is one of the handful of examples to receive the Getrag Group A 5 speed manual gearbox. Other TWR upgrades include: large capacity air intakes and filter elements, special spark plugs and engine management settings, high efficiency stainless steel exhaust with twin tail pipes increasing power to 238 kW, upgraded suspension, body kit which significantly reduces lift and drag , 8” x 16” alloy wheels and much more. Finished in Sage over Rhodium as per the TWR catalogue, the result is a truly purposeful looking car with amazing performance.

For more information on these cars, check out Classic Register's TWR XJ-S information guide, and have a look at the other cars on the TWR XJ-S Register.