Hi Bandjac
This is one of those situtions where there is a simple answer and then a whole picture answer.
The simple answer.
Yes, it'll be easier and cheaper to borrow money on the mortgage. Top up mortgages start at 6 - 7%, your current mortgage would be somewhere in the 5%'s. Since it is 'mortgage' whichever way it is then you are better off taking the cheapest option.
Whole picture answer - this really is where you'd need to speak to a mortgage adviser, but, things to consider are:
Is your current mortgage the best for you - if overpayments are your aim/need, most mortgages allow this, but quite often you pay a higher rate for the benefits of a flexible mortgage. It may be cheaper to look around. Actually, you could include this in the simple answer as well.
If you are maxxed out on credit, has that affected the rates you can achieve? Will overpayments be affordable in the future? If you added the total payments for debt you pay each month what term of mortgage would that come out to? It may be shorter than you expect.
Having said that there are three considerations against this idea - currently your debts are not secured to the house, so if you get into difficulty they can't repossess. Secondly, will the unsecured debts 'reappear' over time. And thirdly, you may be extending the term of the debts.
Hope that helps, give me a call if you want to look at the figures.
Adrian Garside