The buy-to-let sector of the residential property market looks a golden investment as long as house prices keep surging ahead.

Investors buying houses and flats in city centres and suburbs will enjoy rental income and long-term capital gain when they eventually resell.

Figures to be released next month from the Association of Residential Letting Agents (ARLA) are expected to show that £7 billion has been pumped into the sector by the panel of lenders who launched buy-to-let mortgages in 1996.

More than 140,000 loans have been arranged since then. The average loan per property has soared in the past year from £75,000 to nearly £110,000.

One London estate agent in the sector, Ludlow Thompson, says property prices cannot fall in the foreseeable future because investors pile in at the first hint of market weakness.

Thousands of part-time landlords have five properties, while professionals with a dozen or more run them as a full-time job.

Bristol and West (B&W) offers buy-to-let mortgages up to £10 million to buy an instant portfolio for affluent investors with £500,000 of their own cash.

B&W spokesman Bob Perks said there were no repayment problems at this level, although each portfolio was reviewed annually.

So long as the under-30s could not or would not buy - unmarried couples dislike home ownership because breaking-up becomes messier - then buy-to-let investors were on a winner.

ARLA said the private rented sector would grow from 11.3 per cent of total housing stock to 15 per cent in the next few years.

With stock markets slumping and pension performance generally poor, bricks and mortar seemed the surefire investment bound to deliver.

Investors, however, had to get the thing into perspective before they dived in.

A book published last week by actress Fiona Fullerton does just that. She says making money from property can be pretty hard work. You need luck in your timing. In How to Make Money From Property, she writes: "In the old days, lenders penalised borrowers if the property was a second home or was to be let, with the result that only expensive apartments for company directors or cheap bedsits were available.

"Now, however, the middle market has opened up with professional investors like me able to secure special, low-cost mortgages to become the new breed of landlord.

"The most obvious way to make a bigger annual profit is to buy a flat that is in terrible condition, do it up yourself and then let it to a higher-end sort of tenant. This is what I usually do."

How to Make Money From Property by Fiona Fullerton is published by Piatkus Books, of London, at £16.99.