OMG, So much help, thank you guys.
Kacecar, your description is exactly what is happening to mine. I think I might start there with the fuel pump.
I checked the breather pipe and it is clear. I've also got hold of the old owner who said he didn't know of any issues however when he first got her in 2006 she was doing a similar thing. He said the problem was down to a long screw in the top of the engine (fuel) filter that was not undone enough when bleeding the system, by undoing it fully and bleeding the system it resolved the issue. Firstly, this tells me he has only ever had the engine serviced once in 6 years! Not good, but then I have had the engine serviced so this could be the issue, plus no doubt 6 years of debris and gunk running around the fuel tank and fuel system. So the question is, who to get to clean the engine out, is it a mechanic job or something I can do, if I do it do I need specialist tools.
Thank you again, I will feed back when I've had a chance to look into it more.