Well, Mat it will become a bit of an insurance thread - but only because the system means I can hunt down a cheap, reliable small and eco-friendly little 1.1 hatchback, for instance and it'll cost nearly three times to insure as to buy. So it's actually less about finding the right car, more about finding the lowest insurance.
Mind you, it could go horribly wrong:
Found a car that's cheapest to insure at £806.... but it's a Seat Marbella
How about these then:
Renault 5 Campus (1.2) £1,027.59
Ford Fiesta 1.1 LX £1,155.85
Rover 25 1.4 £1,298.95
Rover 200 1.4 £1,391.17 (why more expensive than a 25?)
Peugeot 306 TD £1,399.65
Rover Metro 114 £1,518.37
And, getting silly: a 1994 Nissan Sunny £1,600
1991 Honda Civic £1,764
But someone mentioned a Dyane.
£865.41. Result

(Except a. She wouldn't drive it and b. finding a good one under a couple of grand is hard).