Many thanks to your advice to both ot you, I have found another website that has some really good advice on it
http://www.consumeractiongroup.co.uk/forum/ .
From the information held on that website, the consensus is that I should make an application at the county court to have the statutory demand set aside, request original documents from the debt collector that (a) proves that I owe the amount. (b) they have the right documentation in order to pursue the debt.
Apparently this usually results in the debt collectors not turning up at court therefore they were never serious about enforcing the demand. If they do not provide the documents within a time table it seems that they are commiting an offence and I could then be in the position recovering damages from them!
I know that I owe this money and i am perfectly willing to repay what I owe, from reading what other people have said about the particular debt collector I have to deal with, it is unlikely they would accept my offer and would use quite "ungentlemanlike" tactics to make me pay more.