I've been driving S1's for 35 years.
That one looks too far gone to make sense.
As mentioned by others above, by the time you've fixed this one, you could have bought a nice one finished.
That car will need body work and paint, new fuel tanks and pumps, exhaust, new brakes, suspension work, new battery, those hot-air carb enrichment devises never work, fan shroud, headliner, and more.
Is the steering pump full; leaking rack? Smell gearbox fluid. Pull plugs and do compression test, no-spark could be just points. Coolant full and clean? Trailing arm mounts rusty?

I would buy this car as a parts car and find a better one. You'll be putting several thousand dollars/pounds into this one, so why not see what's out there for the same money that's done.

My first Jag was a '70 XJ6, and everything that could go wrong with a Jag did. I call that one the apprenticeship car.
The second S1 I bought much more carefully and it lasted 36 years.

I hope you get a Jag that suits you.
Rob

 

Great advice from Rob, I drive a 1971 XJ that I have had since the early 90's. It was in great shape then but I have continued to modify and improve since.
It was my second Jag and the first was a S II with lots of hidden rust...floors were gone but were covered on the bottom with heavy undercoating and
on the tops there were pieces of tin and undercoat. I did not know enough to look around THEN. It was so rusty (from Colorado) that the front
harmonic pulley rusted and it broke off the end of the crank!