Although the future trends of house prices are uncertain - with some forecasters predicting financial turbulence ahead - many landlords want to expand their portfolios in the next year.

That is the conclusion of a survey by LSL Property Services, owner of the UK's largest lettings agent network with national chains Your Move and Reeds Rains.

It says 40 per cent of large-scale landlords want to expand their portfolios in the next 12 months, and that 48 per cent of investors believe the buy-to-let market is attractive if they can fix a mortgage. However, only 13 per cent of landlords managed to get a mortgage in the past year.

The survey found that landlords with five or more properties are more likely to increase their involvement in the private rental sector; four in 10 expect their portfolios to grow, compared with 26 per cent of landlords with fewer than five properties.

Almost half (48 per cent) of landlords believe now is a good time to invest in property, consistent with the response of January's sentiment survey (49 per cent). Just two per cent think now is a good time to sell.

Growing tenant demand is driving this optimism. While 46 per cent of larger-scale landlords have seen growing tenant demand, only seven per cent of all respondents saw a decline.

David Brown, commercial director of LSL Property Services, said: "Optimism is flooding back into the buy-to-let market. With total annual returns hitting 13.3 per cent, potential investors see property as a lucrative long-term venture."

Mortgage financing is the big stumbling block. According to the Council of Mortgage Lenders, only 93,500 buy-to-let mortgages were arranged in 2009 - a quarter of 2007 levels.

In the past year, only 23 per cent of large-scale landlords managed to raise new mortgage finance, while 61 per cent found it harder than three years ago - with 28 per cent stating it was much more difficult. Mr Brown added: "Undeniably, the difficulty in obtaining mortgage finance is holding back investment in the private rental sector.

"Over 90 per cent of buy-to-let products have vanished from the market as lenders keep their purse strings drawn tight. Landlords with larger portfolios tend to have larger amounts of equity, and are finding mortgaging distinctly easier than small-scale investors - but lending criteria remain too tight generally."