Landlords are increasingly likely to encounter potential tenants who need a guarantor, since advance rent is no longer available as an additional safeguard.
HomeLet and Let Alliance found that 18.4% of accepted applications required one in July, based on more than one million in-house tenant references.
The proportion has almost doubled from around 9% in January 2025 and is up from 11.4% at the beginning of this year.
Guarantor use surges
Mike Dawson, head of sales at Barbon Insurance Group, said: "Because all this insight comes directly from our own in-house referencing, we have a clear view of how guarantor usage and affordability is changing in real time.
"What we are seeing is that guarantors are no longer the exception and the story behind that shift is affordability."
He added: "In many parts of the country, including London, a typical tenant is now committing a very substantial share of their income to rent when a tenancy begins.
"While Renters’ Rights and the ban on rent in advance have added a further dimension, our data shows this is on top of the longer-term trend."
Affordability pressure builds
Tenants across the UK spent an average of 32.4% of their income on rent when starting a new tenancy in July.
In Greater London, the rent-to-income ratio rose from 35.1% in July 2020 to 38.6% six years later.
The companies said ratios in several higher-cost markets are approaching or exceeding levels typically used by lenders and insurers.
That means applicants falling just outside standard affordability criteria may need a guarantor or similar protection to proceed.
Family support gap
Separate research from LRG suggests tenants without personal guarantors face fewer housing choices despite the availability of professional guarantor services.
Among those unable to rely on relatives or friends, 51% would seek a cheaper property, 16% would stop searching, 18% would use professional support and 15% would select another option.
Allison Thompson, the chief lettings officer at Leaders, part of LRG, said: "Landlords need confidence that a tenancy is affordable and sustainable, particularly now that rent in advance is no longer available as an additional safeguard.
"At the same time, tenants who do not have family or friends able to act as a guarantor should not assume they have run out of options."
Guarantor use for landlords
The managing director of Accommodation for Students, Simon Thompson, said: "It does appear that guarantor reliance is rising, so landlords should review affordability checks before agreeing each tenancy.
"Because of the Renters' Rights Act, advance payments can no longer cover higher-risk applicants, making alternative income protection increasingly relevant.
"While tenants who lack family support may abandon searches or choose cheaper homes, a guarantor may help widen access while giving landlords greater confidence over arrears exposure."
