What are the rules on renting out a leasehold flat?
Renting out a flat you own leasehold is governed by your lease first, and the lease frequently restricts or conditions subletting in ways owners discover only when they try — or worse, after they have already let it.
What the lease typically says, and you must read your own:
An absolute prohibition on subletting, which is uncommon but does exist and cannot simply be ignored.
A requirement for landlord consent, often with a statutory gloss that consent must not be unreasonably withheld.
A notice requirement, obliging you to notify the freeholder or managing agent of any letting within a set period, usually with a fee.
Restrictions on the type of letting — commonly prohibiting short-term or holiday letting, or requiring a minimum term such as six or twelve months.
A covenant against use other than as a private dwelling, which has repeatedly been held to prohibit short-term holiday letting even where subletting generally is permitted.
Breaching the lease is serious. It can lead to a claim for breach of covenant, liability for the freeholder's costs, difficulty selling, and in principle forfeiture — and it will almost certainly be discovered at sale, when the buyer's solicitor requests the management pack.
What else applies beyond the lease:
Your mortgage. A residential mortgage generally prohibits letting without consent to let, and letting without it is a breach of the mortgage conditions.
Insurance. The building insurance is usually the freeholder's, but your own contents and liability cover changes, and the freeholder's policy may require notification of letting.
All the ordinary landlord obligations — deposit protection, gas and electrical safety, right to rent checks, energy performance requirements, and licensing where the property falls within a selective or HMO scheme.
Local short-let rules, including registration schemes and planning restrictions in some areas, which apply independently of the lease.
Ground rent and service charge remain yours, regardless of the tenant.
Practical advice: obtain written consent, keep it with the deeds, and budget for the freeholder's administration fees.
General information, not legal advice.