What's the problem?
Earlier this year, I tried to remortgage.
With a good credit record, 3 years of accounts, a contract in hand (ie. decent forward order book), a building society and my own bank were happy to lend.
My bank mostly lends from customer deposits, so I wouldn't want them lending my money to someone who can't prove they can pay it back.
If you're thinking of going contracting, sort out your mortgage before you start, and if you don't have one, spend the 2-3 years you need to prove yourself saving a better deposit.