UK Economy

The main driver is inflation - it's higher than expected, and not falling as fast as expected. So bond yields have gone up as the market expects Interest Rates to go up further to bring down inflation.

The problem for the mortgage lenders is that they themselves borrow money off the market - if they offer a product at 5.5% but their own borrowing rate goes up, they're at risk of losing money if people fix at the low rate. These changes are happening fast at the moment causing the mortgage lenders to be inundated with demand and then discovering their product is no longer even viable.

This will calm down once Inflation starts falling in line with predictions (rather than defying predictions); bond markets will become less volatile and more predictable so mortgage lenders will be able to offer deals for longer without worrying their costs will change by the next day.