In a further sign of Scotland's rural housing shortage, Perth & Kinross yesterday became the seventh council to suspend the right to buy (RTB) for its tenants in an effort to preserve its ever-dwindling stock.

Since the RTB was introduced by Mrs Thatcher's government 25 years ago, around 500,000 council houses have been bought by tenants in Scotland.

Across Perth & Kinross as a whole, some 42% have been sold; in Highland Perthshire the loss exceeds 50%. Last year, the council saw a further 218 RTB sales, eroding its stock below the 8000 mark.

Approval from Scottish ministers yesterday means the council can now suspend RTB for five years in 21 "pressured areas" where there are an average of five people on the housing waiting list for each vacant council let.

The move will affect around 600 tenants - half of them existing tenants who moved into homes after September 2002, and the others prospective tenants.

The pressured areas fall into two broad varieties - those in Highland Perthshire, where turnover is slow, and the commuter areas of "Greater Perth", where demand is high.

The latter group includes Scone, Methven, Balbeggie, Glenfarg, Abernethy and Bridge of Earn, where the building of a rash of new owner-occupied homes is creating a knock-on demand for ex-council houses as the area becomes more popular. The highland areas include Blair Atholl, Pitlochry, Aberfeldy and Kinloch Rannoch.

Anne Begg, centre manager at Perthshire Solicitors Property Centre, said the council's decision was understandable as the housing market was "crazy". With prices up 13% last year, the average house sells for £160,000, and the average villa for £243,000.

The average council home can be bought for a long-sitting tenant for around £50,000. Ms Begg said ex-council houses were selling for around £110,000. "They've become the new starter homes for families," she said.

James Jopling, of the housing charity Shelter, welcomed Perth & Kinross's decision.

He said: "We need more affordable housing not just in Perth & Kinross but across Scotland as a whole - that's why we're urging the Scottish Executive to commit significantly more money for it."

Communities Minister Rhona Brankin said Perth & Kinross has presented "compelling evidence of substantial pressures" on affordable housing.