If you must have one, better to get a petrol. But a far better idea would be to get something else entirely, something better, more reliable and cheaper to run.

For your budget stick to petrol. FInd one that has a good service history, if you can. Look for condition and service., but mileage is also important. At this price level you could end up with some big bills so it is a bit of a lottery. Buy the best car you can afford.

I found the 1-series a small car, if that suits you thats fine, I would go for something a bit bigger, even a Focus/Astra is more practical. Some good Japanese or Korean cars will be in your budget. A Toyota Auris 1.4/1.6 petrol is in your budget, 2012, or a VX Astra 1.4 or 1.6i 2013. I would stick with the 1.6 engine, as a 1.4 engine can struggle and the petrol savings are not huge. The biggest MPG difference is how you drive it.

If you are not familar buying cars then take along a friend or family member who is more knowledgeable, and help avoid buying a money pit. Good Luck.

I'll echo the sentiment that a BMW at your budget is just asking for trouble. Stick to naturally-aspirated Japanese petrol engines.

A BMW that's been well looked after and regularly serviced will last a long time: but one that hasn't can be a money-pit. You have to take a chance on how previous owners drove a car, but you should of course look for one with a full service history, ideally serviced at a BMW dealer or a specialist.

Unless you're going to do a very high mileage, go for petrol rather than diesel: ageing diesels can go very expensively wrong. Unfortunately when cars of the age you're buying were new, people were being encouraged to buy diesels, so petrols are harder to find.

There are of course many alternatives to a 1-series. Japanese cars like Toyotas, Hondas and and Mazdas are less prestigious but give you a better chance of getting a good one. But that probably isn't what you want.

Probably best to buy from a dealer, as you have more in the way of legal consumer protection. Ideally look for a car that's done between 6,000 and 12,000 miles a year - not too low and not too high. Generally the fewer owners the better: someone who has kept the car for several years will probably have liked it.

Finally, look up the 1-series in the car-by-car reviews on this site, and see what to look out for in particular.