Tax and regulatory changes have caused some 222,500 landlords to sell up and leave the sector since 2017, according to estimates by estate agent Hamptons International.

There are now 2.66 million buy-to-let investors in the UK, a fall of eight per cent in just two years.

At the same time, the total number of privately rented homes has fallen by 156,410.

However, the average investor portfolio has increased to 1.93 – a level not seen since 2009.

Average rents increased to £998 per month in January, a 3.6 per cent jump from the same period last year.

The research showed landlords in the North East had the biggest portfolios, typically owning 2.05 homes on average, followed by those in Yorkshire & the Humber, and London.

Investors in Wales and Scotland were least likely to have big buy-to-let portfolios.

Rents continued to increase the most in the South West, up six per cent, followed by the East and Greater London, both at 4.1 per cent.

Aneisha Beveridge, head of research at Hamptons International, said: “The number of landlords in the private rented sector has fallen to the lowest level in seven years.

“While 222,570 landlords have left the sector since 2017 due to tax and regulatory changes, those who have stayed tend to have bigger portfolios – a further sign that the sector is professionalising. The average landlord in Great Britain owned 1.93 properties last year, the highest level since 2009.

“Rents rose in every region across Great Britain in January to stand 3.6 per cent higher than at the same time last year. The number of new homes purchased by landlords remains low, which is feeding through to fewer homes available to rent. This is particularly true in the South, where rents are rising the most.”