John Lewis.
Bikes under £1000 are covered automatically. Over 1k you have to declare them.
There's no ridiculous restrictions on where/how they have to be locked up etc.
We had cause to make a claim a year or too ago, an assessor visited 2 days after the theft, and we had a cheque within the week for the full insured amount - no quibbles or problems.
The following years insurance was slightly more expensive, but not stupidly so, and a subsequent renewal didnt break the bank either.
All round very impressed with them.