I looked into this a long time ago, house insurance is the cheapest and sometimes costs nothing at all to insure your bike
whilst its at home. My bikes ( the family has 13 all together) are on our direct line house policy we pay a whole 20 quid more for the more expensive bikes. It only insures them if stolen from the house, it is great though as new for old.We had 2 bikes stolen last year , they paid up no fuss at all. To insure them away from the house is prohibitive, as
@BrynCP said One bike of say 1800 value would cost about150 quid a year, this is Essex may be cheaper somewhere else. I can insure a mororbike or car for that. I have insured a new bike before but after the first year it was not worth it as I found the companies I looked at devalued its replacement by nearly 50%. Also there were so many rules, Gold standard lock, must show the keys and reciept for the lock if bike stolen. Of course I have had a bike stolen ( from work) with no insurance. Was 6 months old and put me 800 quid out of pocket.( had cctv of the thief, police would not even look at it cos black and white footage) At that point I would have wished it insured but we have so many bikes it was not worth insuring them all as the cost of insuring them I could have bought a very good bike every month.
As your bikes are new it may be worth insuring them for the first year at least. If your bike was in Essex I think you would be looking at say 150 per year plus 150 for a gold standard lock. Which is bloody heavy and you are not going to want to carry with you anyway so kind of pointless.