I looked extensively at different options, but for the number of bikes I have the best option worked out to be Cyclecover. A lot of others require you to list bikes individually; one even had a clause that if your bike is modified "from the manufacturers specifications", they have the right to deny the claim. ie, if you even change say a saddle, or cassette, they had the right to say "nup, breaches this clause". I quickly queried them about this, then raised it with the ombudsman when they didn't care, which I believe resulted in a 5 figure fine.
Be careful of dodgy clauses like that.