The buy-to-let sector significantly increased its share of total mortgage advances again in the third quarter of this year as investors shunned equities and tired of low interest rates on their cash savings.

Latest figures from the Council of Mortgage Lenders show that a total of 34,500 buy-to-let mortgages were advanced in the third quarter - up 16.2% on the figure for quarter two and the highest number of buy-to-let advances since the final quarter of 2008.

The value of buy-to-let lending also rose, by 18.8% quarter-on-quarter, to £3.8 billion.

However, some commentators say the trend won't be sustained.

Paul Diggle, at Capital Economics, says: "While this trend probably has further to run, we don't think lending to the sector can escape signs of renewed economic weakness unscathed.

"The recovery in the buy-to-let sector means that, at 10.7%, buy-to-let's share of total mortgage advances by value is at its highest level in three years. As a share of the outstanding stock of mortgages, buy-to-let hit a new peak of 12.6% in value in the third quarter."

Thanks to a blend of rising rents, cheap mortgages and very short void periods between tenants, the number of landlords in financial trouble is remarkably low.

Latest data also shows a small improvement in the number of buy-to-let borrowers at least three months in arrears - while the share of repossessions held steady at a three-year low of 0.08%.

But Paul is hardly throwing his hat in the air.

"The outlook for buy-to-let lending is difficult to read.

"On the one hand, with credit conditions in the owner-occupier mortgage market still tight, there is unlikely to be an easing in tenant demand anytime soon. That should support the number of buy-to-let advances.

"However, we find it hard to believe landlords are immune from the signs of renewed weakness in the housing market and the wider economy. On balance, the pace of growth in buy-to-let advances should slow from here."

As demand for rental properties outstrips supply and the average length of tenure hits a record high, experienced landlords may also be playing a canny game, by investing in cheaper areas of the country.