The depreciation on the Astra will make the Alfa's fuel bill appear a bargain. You've seen how much it has depreciated already, and at that age it's still on the very steep part of the curve.
You do have the warranty so largely worry free motoring for a few years, but that doesn't come cheap even if it is a "sensible" car.
Maybe you're too in love with FWD after being wooed by the Alfa to consider coming back to meega ownership 
No Paul. I'm in love with trying to hang on to some of my hard-earned. 
Surely then spending £8000 on a nearly new car that will depreciate loads over the next few years isn't the best approach? It's nice having a warranty and an economical engine, but unless you do huge mileage or keep the car for many years, it would be far cheaper in overall terms to buy something like a 2003 V6 Omega. It's been through the worst of its savage depreciation, so you're getting a lot more car for a lot less money. It costs more to run, but unless you're very unlucky and have a major failure, it's still going to be a lot cheaper as it will lose less value. Even more so if you're paying for the new car with credit.
I've had a few cars more expensive than £8k, but of those I've never got less than 90% of what I paid come resale. Mainly because I only pay significant amounts of money for "fun" cars, that tend to be a bit rarer and more desirable. It helps that I'm not using them every day of course, keeping the mileage down. For the daily chores, I'd rather have a cheap runaround, perfect example being the 2.0 Audi I put about 50,000 miles onto over the course of 3 years, and sold for only £300 less than I paid for it. Add to that it was peanuts to run (all the parts were cheap from Euro Car Parts and it never broke down), and that is the perfect example of cheap motoring! I was sorry to see it go, but the lack of power (only about 115 BHP) and front wheel drive were the two things I really disliked about it, and the main reason I bought a 3.0 Omega for my runaround.