The offset idea is simple. Borrowers' cash savings are set against their mortgage debt, so they pay interest only on the balance. But monthly mortgage repayments are calculated on the full debt, before offsetting is taken into account. So borrowers effectively overpay on their debt each month.

That means the mortgage debt is cleared much faster than with a conventional loan. And borrowers benefit from not paying tax on the interest they would otherwise earn on their savings.

So, for example, a borrower with a £100,000 mortgage paying Intelligent Finance's offset tracker loan rate of 5.24% would save more than £39,000 interest over the life of the mortgage by offsetting £20,000 of savings. They would also pay off the loan five years early, based on a traditional 25 year mortgage.