Some contents insurance plans include bicycle cover, either as standard or as an extra you can bolt on for an additional charge on your premiums. When you compare home insurance, read the fine print of any policy to see if they cover bicycles.
Some contents insurance policies limit cover for bicycles to well below what a high-end bike would cost to replace, so it's important to double check what you're covered for, and increase is as necessary.
Home insurance policies can also have excesses that may exceed the cost of your bicycle. If your bicycle is stolen separately, rather than being damaged or lost as part of a wider disaster or burglary, you may have to cover its repair or replacement entirely yourself, under the limit of your excess.
Some of these policies won't cover your bicycle when it's out of the house and if they do, they often won't provide extras like personal accident and public liability cover. For that, you'll need a specialist cycling insurance policy.
Finally, claiming for the bike theft or damage will damage your no claims bonus, meaning your home contents insurance policy will cost more when it comes up for renewal.