I got my renewal quote from M&S which was very high this year. I got a quote from John Lewis that was just over half the price. I had to specify all bikes over a grand, which I did.
Unfortunately I have had to test the insurance recently as we got our shed robbed. Fortunately, I found John Lewis to be excellent. They replaced my partner’s road bike with the current model immediately. For my mountain bike I sent a spreadsheet in with the list of components (most of which I had purchased 2nd hand) and they calculated the cost of all the items new, and transferred the money straight into my bank account (£2,200 even though I had only specified the bike to be worth £2k).
When M&S renew, get yourself a quote from JL to see how it matches up – I’d highly recommend them.