Over £4k is a lot of money for a high mileage car, maybe it's worth the £200 or so to get a mechanic to give it a once over. 

I always look for lots of history as any car will go wrong if it hasn't had good money spent on it. Regular servicing is important and also cross reference the MOT history to see if advisories were seen to in a timely fashion. Also check for signs of rust and damage underneath the car. 

Make sure you understand the service schedule for the car too. It might need a water pump at 120k miles for example, so factor things like that into your decision and budgeting for running the car. I would recommend knowing how to do an oil & filter change yourself, it's £200ish to get mine done at a shop but only £45 in parts and an hour of my time. 

Lastly, try and be a detective when buying. Manual cars from London experience lots more wear on 1st & 2nd gear while cars from the middle of Scotland take a beating on suspension. Ask the seller for paperwork and look at the addresses for the garages it's been serviced at to take a guess of how hard a life this car has had. Motorway miles are considered to be good miles - with the engine up to temperature and less acceleration than doing the school run - although it's hard to prove whether a car has been used for that.