If you're in the fortunate position of being able to afford a mortgage over £300,000 and have at least a 40% deposit, then the Post Office are offering a 2-year fixed deal at an initial rate of just 1.37%!
Comes with an arrangement fee of £1,995 and a lending fee of £195 - payment of the latter can be deferred until your mortgage is fully repaid.
That's approximately the figure that an online mortgage calculator tool shows is the minimum necessary to end up cheaper than the 1.99% no fee deal that's currently ultra-hot. The larger the mortgage, the more the saving. At the extreme top end (£1,000,000 which is the Post Office limit) you would save nearly £6,000 during the 2-year fixed period by selecting this 1.37% rate and paying the arrangement fee vs going for the fee-free 1.99% rate.