With asking prices for rents at a new record, more landlords are planning to raise their investment in the sector than quit.

A third of landlords are planning to increase their portfolios. However, a quarter of landlords are planning to reduce them.

There is already a shortage of new rental stock, Rightmove reported this morning.

It said that tax changes are deterring both new and existing landlords.

Rightmove also cited as deterrents the Stamp Duty surcharge on the purchase of second homes and the ban on tenants fees which some agents may be passing on to landlords.

Coupled with strong demand from tenants, there are record asking rents across all parts of Britain except for Scotland and the north east.

Rightmove said there was some evidence that tenants are paying the price of the fees ban, in terms of higher rents.

Asking rents outside London are at a new peak of £828 per calendar month – representing the biggest quarterly jump at this time of year since 2015.

Within London, rents are at a record of £2,104 on average per month – the biggest quarterly jump since Rightmove began recording the data.

These latest increases mean an annual rate of growth of 3.2% outside London, and of 5.6% within London.

Nationally, the number of available rental properties is 13% under its previous low in the third quarter of 2015, and 24% down in London.

Rightmove has asked landlords about their intentions.

Almost a quarter, 24%, said they are planning to sell at least one property, including 11% who say they plan to sell their entire portfolios.

Landlords told Rightmove that their reasons for selling up are the tax relief changes and the tenants fee ban.

The average landlord in the study lets three properties, with a quarter owning just one.

Of the 30% planning to increase their portfolios, most say that property still delivers better returns than other investments.

Rightmove housing expert Miles Shipside said: “There are a number of forces at play in the current rental market, all leading to record rents for tenants and fewer homes to choose from, yet demand remains strong.

“Worryingly for tenants there are signs that the stock shortage may worsen if some landlords follow through with their plans to sell up.

“The overall feeling among those landlords who are planning to exit the market is one of frustration with many telling us that the tax changes mean it’s no longer financially attractive to keep their properties.

“Early data seems to point to some of the income lost through the removal of tenant fees being passed on to the tenant in higher rents.

“Rising rents may tempt some landlords back in, but momentum is currently to downsize portfolios in spite of the prospect of increasing yields.”

One agent, Clynton Nel, at JOHNS&CO, told Rightmove: “We know of some investors who bought just prior to the referendum a few years ago who today are supplementing their investment with their cash each month as it is simply unprofitable right now.

“They don’t wish to exit because they may not yet have the gains they would want, but they see the opportunity in the longer term.”