Get an AA check done.
If ok, consider buying it and get a P3 service done.
Bear in mind that those two things will probably set you back £500-£600 depending on where you are in the country. The AA check may hightlight other things that need replacing meaning that your £6500 car could be a £7500+ car quite quickly.
If you think you might keep it 3 or 4 years then it could be a bargain, as you could build up a service history. If you might punt it on in 6-12 months then you could find it hard to shift.
I wouldn't rule it out, but for me, i'd want it cheaper than £6500 as there are plenty of decent UK GT's for less than £8k....