Ok, I have a question for you.
Let’s imagine you’re in the same situation but instead of markets falling, they’re rising. What would you think if the sellers came back to you this late in the process and asked for another £20k to reflect the change in the market price?
Your response to this provides your answer.
If you think it’s fair that you should have an offer accepted and then suddenly when you’re close to exchanging, the sellers ask for more - then crack on and drop your offer.
If you’d have felt aggrieved at the sellers asking for more money, then it’s equally unfair that you now ask to pay less.
If you absolutely believe that you’re paying a ridiculously high price then you might need to consider it. You shouldn’t buy a house out of politeness.
However, as a general rule both gazumping and gazundering are rotten things to do. If you have to do so, you should have an extremely good reason because it’s a shitty thing to do.
Do make sure you’re certain about the survey though. We thought our surveyor was being a bit over-cautious too and it was fine. We didn’t ask for a reduction either - but this was last summer and there were buyers queuing up to take our place!