Some 307 letting agency branches across London, handling some 115,000 homes, are now badged under the Mayor's London Rental Standard accreditation service.
The Mayor's office says it has been adopted by many of the biggest names in the lettings industry including Spicerhaart, Haart and Felicity J Lord; Andrews; CBRE; Chestertons; Douglas and Gordon; Savills; Knight Frank; Leaders; Foxtons; and Stirling Ackroyd.
To sign up the branches must provide evidence that they offer transparent fees and good property conditions, communications between landlords and tenants, improved response times and repairs, and protected deposits.
Thirty per cent of London's households now live in rented homes, and by the mid-2020s the number of renters is predicted to overtake the number of homeowners in the capital. In the last ten years the number of families with children renting in London has risen 10 per cent to almost a third.
However, a survey by the Mayor's office suggests 85 per cent of landlords are not aware of core legislation that protects renters and 61 per cent have no professional management training.
Now Boris Johnson says all remaining letting agents and landlords should sign up to the standard which he claims is improving the experience of everyone involved with a clear code of good practice.
Lori Thompson, director of customer services and compliance at Foxtons, says: "As part of our accreditation, all our senior lettings employees have undertaken intensive training courses achieving NALS or ARLA qualifications and we encourage other lettings agents to join the London Rental Standard benefitting their customers and employees alike."
The standard has now been supported by firms operating within the sector too, including Endsleigh Insurance, MyDeposits and EasyRoommate.com which offer incentives to landlords and agents to encourage them to sign up.
Since its inception last spring the standard scheme has been backed by ARLA, RICS, NALS and UKALA.