As the badging suggests, this car is a Biturbo i, its too early to be a 222 as they weren't introduced until 1988. This family of cars are known generically as the Biturbo II and feature a few updates over the first series cars including aerodynamic door mirrors, the later type seats as opposed to the earlier flatter style, rounded instrument binnacle to replace the large rectangular one etc. The Biturbo i was originally produced only for the domestic market so it should have a 2 litre version of the v6, perhaps the presence of fuel injection has confused you Ewan?
As far as values go, the early biturbos are not hugely sought after, some purists like the really early first series cars but generally speaking an earlyish Biturbo isn't going to be worth much more than £6-7k. There are a few models that are becoming collectible however, the Biturbo Si & Si Black are very sought after in Italy. This car is unusual in that it is an early car with fuel injection but i don't think its worth a premium over a carb version as it isn't much different spec wise.
I don't think £4k is too bad, i wouldn't get too hung up on service history as these cars are quite tough mechanically, I'd be more concerned about the bodywork. If that's ok then it'd be worth a punt, if the engine turns out not to be any good you could find a used one for £500 or so, a good opportunity to drop in a 2.8. You wouldn't see much of a gain in value over time but it'd be a cheap quick little car.