The engineers generally will not have any knowledge other than the line itself (connecting to your PC isn't part of it) as they were never trained to do so, especially Openreach's pol;icy is "up to the wall plug" (NTE), as long as they plug their laptop in and it works there, they don't need to know whether it works on your PC or not. He wouldn't know what is wrong speed wise, he would need to call the OMC (where I used to work) and we have to do the line test, analyse the result, then tell them the potential issues and then they go and try to locate them.
And yes if you go to London, 100MB Virgin line!!!!!!
I am getting one when I have more spare cash lying around for nothing :P