Home insurance for landlord purposes is the commonest expensive mistake in this part of the market, and it is usually made in good faith. An owner moves out, lets the house, and leaves the existing policy running because nothing about the building has changed. What has changed is who lives there, and that is the thing household policies are written around.
What the household policy actually says
Almost every UK home policy is written for a property occupied by the policyholder and their household, and either excludes letting outright or requires the insurer's agreement. Letting without telling them is a change to the risk that was not disclosed, which gives the insurer grounds to reduce or decline a claim, however unrelated the loss.
What it does not cover even if it did respond
Loss of rent. Property owners liability as a landlord to a tenant. Damage by a tenant, accidental or malicious. Longer void periods between tenancies. Landlord contents as a category. The absence of these is not a technicality: they are the things that go wrong in a let property.
What to do instead
Tell the insurer the property is being let and either move to their landlord product or to another insurer's. The switch is routine and the premium difference is usually modest. Where the property is a leasehold flat, the right purchase is a flat landlord policy without a buildings section, because the freeholder insures the structure.
If you have already been letting on a home policy
Tell the insurer now rather than at renewal. Disclosing late is far better than having a claim declined, and most insurers will simply move the policy. Carrying on and hoping is a bet on nothing going wrong for the rest of the tenancy, which is a bet with a large downside and no upside.
Questions people ask about home insurance for landlord
Can I let my house on my home insurance?
Almost never. Household policies are written for owner occupied property and exclude letting or require the insurer's agreement.
What happens if I claim while letting on a home policy?
The insurer may reduce or decline the claim because the risk was not what was disclosed, even where the loss is unrelated to the letting.
What should I switch to?
A landlord policy, or for a leasehold flat a flat landlord policy without a buildings section because the freeholder insures the structure.
I have been letting for a year already. What now?
Tell the insurer now rather than at renewal. Late disclosure is far better than a declined claim, and most insurers will simply move the policy.