This means that instead of earning interest on your savings, you pay less interest on your mortgage. So, for example, if you have a mortgage of £125,000 and you have £25,000 in your linked accounts, then your monthly mortgage interest would be calculated on £100,000 instead of the balance of £125,000.
Whilst an offset mortgage can save you money and shorten your mortgage term, they can be more expensive than comparable deals, and there may be less choice available.
As a mortgage is secured against your home, it could be repossessed if you do not keep up the mortgage repayments.