Oddly when Nationwide changed underwriter to UK Insurance (aka Direct Line), I seemed to gain cover.
Before I was not getting specific bike cover, only vague cover under personal possessions but there was a separate additional cover I could pay for specifically for bikes (and not much at that). Now they’ve automatically covered me for bikes. Okay it’s £1k max they’ll pay out on a bike, though it is per bike and up to £5k, including away from home and overseas. That’s without specifying a bike. I haven’t tried yet but might do to see if they’ll bump it up for not too much more.
I’m a bit stuck with household insurers though as my road floods outside my house once every 10 or 20 years, and though the house never has, most insurers say “computer says no”, or charge a fortune. Nationwide didn’t seem bothered and insured me fine for not too much beyond the cheapies.