A very good move, and a good way to build your score, the trick is to pay them off each month therefore saving a shed load of interest charges........

That isn't the way to build up your score, you need to leave a little bit each month, let it build up then pay it off.
If you pay it off in full each month then you haven't actually 'borrowed' anything and the score won't increase.
This I know for a fact as in the mid 90's my family had been running their own business for years and it worked on an overdraft facility of up to £80k, the bank decided they needed security and were going to remove the overdraft facility. So my parents had to take out a mortgage on their house, which would become a directors loan to the company and keep Barclays happy. My parents were lucky, thanks to the family building business they built their house without the need for any borrowing, also being given the land as a wedding present helped.
They wanted to borrow £80k on a house valued at over £350k (it was two houses 'joined' together thet could be split and sold individually which made it slightly more complicated), they went to couple of companies with personal bank statements for years that showed they were never overdrawn and both Barclaycards were paid off in full every month.
They were given a zero credit rating as they had never 'borrowed' anything.