Its buy-to-let index revealed that the average rent in England and Wales rose by 0.5% to £696 a month in May, surpassing the previous high in April of £692.
The growth means that the average rent was £30 a month higher than May 2010, an annual inflation rate of 4.4%.
The average yield remained at a record high of 5.1% in May.
However, LSL figures showed that there are significant regional differences, with London rents growing 7.8% in the past year, while the East of England suffered average rental decreases of 1.2%.
Nevertheless, in the past 12 months, all but two regions in England and Wales have seen rents increase.
LSL found that, while tenant arrears decreased in May, they remain high at 11.5% of all UK rent unpaid or late by the end of the month.
Unpaid rent totalled £277m across the UK in May, a decrease of 2.5% from the £284m unpaid in April.
David Brown, commercial director of LSL Property Services, said: “The rocketing cost of living, combined with ongoing difficulty first-time buyers are experiencing in obtaining a mortgage is increasing the number reliant on rental accommodation.
“With the fierce competition for homes, rental gazumping is becoming more commonplace and properties are being let beyond asking price, putting further upwards pressure on the market.
“For tenants unable to buy, renting is becoming less affordable as demand booms. Rents are increasing at twice the rate of wages.”
He added: “Tenant finances are coming under increasing strain from rampant inflation and soaring rents. The labour market has remained surprisingly robust, but public sector job losses will begin to have a deeper impact on many tenants’ finances as the year progresses.”
Brown warned that landlords must react quickly to any potential payment problems to prevent tenant arrears spiralling out of control.
John Heron, Paragon Mortgages managing director, said that the rising rent costs give an indication of the continued lack of properties in the buy-to-let sector due to the constrained finances of professional landlords.
“There are a number of products available for smaller scale landlords, with only one or two properties, but for the professional landlord with a large portfolio there is limited finance available.”
He added: “Whilst we are seeing a gradual growth in the number of buy-to-let products available, more are needed because it is the professional landlord that is going to drive the growth in this sector.”
