I have a pair of size 7 (40) sidi vertigo boots that you could borrow. I'm in Chippenham.
I am not certain they would fit you.

As others have said you should push back on the retailer and show them you know your rights. Quote the sales of goods act at them and don't let them fobb you off. Not having your boots will potentially prevent "life changing" injuries so I think that comes under the category of "significant inconvenience".

Under the Sale of Goods Act, the retailer must either repair or replace the goods 'within a reasonable time but without causing significant inconvenience'.
I'm happy to lend you mine as I have others pairs I can use, but you'd obviously need to collect and bring them back which is about 100 miles all in.
Hopefully you'll get a better offer.