Thanks for the responses.
I asked the people who live in the house nearest to the one we are thinking of buying what their speed was and it's
3.12Mbps down and 0.64Mbps up.
Worse than where I currently live.
I'm guessing the show home must be a leased line from perhaps the Prestwick exchange.
Will see if the sales people can get me in touch with the companies IT department to clarify.