Just do a thought experiment, OP. Imagine your buyer was buying with 10% down, with a 25 year mortgage.
If you had sold last winter, when the average mortgage was at around 2.5%, their payment would have been roughly £2800/month.
Now, at 5.5% mortgage, the same payment is £3870/month.
Even if they had the same exact deposit saved (£79k), then to get the same mortgage of £2800/month, the price of the house would have to be £540,000.
That's what the difference in the mortgage rates does. It makes a person who could afford a £700,000 house last January be able only to afford a £540,000 house in December.
So:
a) the idea that you think this wouldn't affect the housing market is batshit.
b) the idea that a reasonable offer, of less than 10% off asking, is an insult, is even worse.
c) and the idea that you're taking house selling personally, rather than as a business transaction, means that you're going to have a miserable experience.