Clarification on the impact of a change in the Bank Rate (UK)
Interest rates in commercial banks are determined by market forces - supply and demand.

Their demand will be influenced by their customers' expectations - which will be influenced by the Central Bank interest rate. Their supply will be influenced by the Central Bank (the Bank of England) interest rate.

Some UK mortgages have fixed interest rates for a particular term - for example, the first three or five years of the mortgage. After that, they revert to the standard variable rate, which loosely tracks the Central Bank interest rate plus a few percentage points.

Some UK mortgages are trackers - that is to say, they are designed so that they track the Central Bank interest rate plus a fixed offset, and they change very quickly when Central Bank rates change: if the Central Bank rate changes by x%, then within one day to one month, the tracker interest rates also change by x%.