Westminster City Council is currently investigating 2,712 properties suspected of operating as unlawful short-term lets, in what represents a significant escalation of enforcement action across some of the capital’s most prized investment postcodes.
The figures, accurate as of 30 March 2026, come as Whitehall prepares to switch on a long-awaited registration scheme designed to bring the booming short-let sector under tighter control, a development with material implications for the thousands of landlords and investors active in the London market.
Data obtained through a tranche of Freedom of Information requests submitted by the Property Buying Company show that Westminster opened 499 fresh short-term letting investigations during 2025 in connection with suspected breaches of the so-called 90-night rule. Under the rule, owners of London property may legally let their homes on a short-term basis for no more than 90 nights in any calendar year. Beyond that threshold, planning permission must be sought from the local authority for a change of use.
Twenty-two formal enforcement notices were served by the council during the same period, with a further 36 in draft, a marked uplift on 2024, when only two properties were served notice despite 469 investigations being opened.
The 90-night cap was introduced to protect Londoners’ housing stock and to mitigate the nuisance issues, noise, anti-social behaviour, fly-tipping, that have come to dog amenity-sensitive boroughs since the rapid rise of platforms such as Airbnb. For investors, the rule has long sat at the heart of the buy-to-let-versus-short-let calculation, and tighter enforcement is poised to alter the yield equation in central London.
The Property Buying Company’s research shows that Tower Hamlets Borough Council investigated 24 properties during 2025, of which eight were found to be in breach. That compares with 35 investigations and just three confirmed breaches in 2024. Hounslow, meanwhile, recorded ten properties in breach of the 90-night rule over the course of last year.
While the headline numbers remain modest in some boroughs, the trend is unmistakable: town halls are sharpening their enforcement tools at precisely the moment central government is preparing to hand them a much bigger one.
Discussions on the design of the new short-term let property register are already advanced, with a launch date expected to be confirmed later this year. The Government has yet to decide whether the scheme will be rolled out simultaneously across England, with the relevant secondary legislation still working its way through Parliament.
For investors, the register promises a level of clarity the sector has hitherto lacked. By tracking the number of nights for which each property is let, councils will, in theory, find it considerably easier to prove a breach and to follow through with enforcement action.
Jonny Christie, co-founder of the Property Buying Company, said the direction of travel was overdue.
“Losing a vast number of homes to short-term lets is a significant problem nationally and particularly in London,” he said. “It’s encouraging to see that discussions are in place to take steps to tackle the issue with a short-term let property register.
“If your property is registered as a residential home, where council tax applies, you can host short-term lets for up to 90 nights. If you exceed 90 nights, you must contact your local council to apply for planning permission to change your property’s use to a holiday rental or serviced apartment.”
For portfolio landlords weighing the relative merits of assured shorthold tenancies against the higher headline yields available from the short-let market, the message from Westminster is clear: the days of operating in the regulatory shadows are numbered. With enforcement intensifying, notices being drafted in greater volume, and a statutory register on the horizon, investors banking on short-let income in central London would be well advised to stress-test their numbers against a 90-night ceiling, and to factor in the cost, time and uncertainty of pursuing a planning application should they wish to exceed it.
