Boarding fees at Scotland's leading private schools have risen by 81% over the past 10 years, a new survey shows.

Average boarding fees north of the border have risen from £11,304 in 1997 to £20,463 last year, according to analysis of figures from the UK-wide Independent Schools Council by the Bank of Scotland.

Across the UK over the same period, private school fees for boarders increased by an average of 86%, nearly three times the increase in the Retail Price Index. Fees are highest in London, at £23,250.

The Bank of Scotland study also found that a boarding school education has become less affordable in terms of average earnings.

Ten years ago there were seven professions for whom average boarding fees amounted to one-quarter of their earnings - seen as a significant measure of affordability by the Bank of Scotland. In 2007 only one occupation remains in that category - directors and chief executive of major organisations - with brokers, doctors, pilots and financial managers all dropping out.

For public sector workers such as teachers, nurses, police officers and fire officers, annual boarding school fees would amount to between 57% and 75% of their salaries.

However, despite the steep rise in fees outlined in the report, the figures on admissions show that numbers seeking boarding places at Scottish schools are actually rising.

The Scottish Council for Independent Schools (SCIS) said that although boarding pupils fell from 4295 in 1997 to 3312 in 2005, since then they rose to 3596 last year.

Judith Sischy, director of SCIS, said: "We recognise the significant financial commitment made by parents for boarding school fees, but residential provision in any school is inevitably expensive as it has to cover not only tuition costs, but also all-round care and welfare.

"Day and boarding schools try to keep their fees as low as possible and will provide financial assistance in cases of need wherever possible.

"Boarding schools form an important part of the sector in Scotland and offer a caring, friendly and family environment away from home."

Martin Ellis, an economist at Bank of Scotland, said: "Boarding school fees have risen by significantly more than average earnings over the past five years.

"This shows how important it is for parents to plan their finances as early as possible if they want to send their children to boarding school."

Bank of Scotland said their research had also shown that schools were increasingly seeking to ease the affordability difficulties by increasing the number of bursaries available.

Nearly one-third of pupils at independent schools across the UK now receive support worth over £300m. The proportion receiving bursaries has increased significantly since 2000 when 20% of pupils received support from the school.

The high fees charged to parents is one of the reasons why there have been calls for private schools to lose their status as charities. In February it emerged that Scotland's 17 leading independent schools have a combined annual income of more than £160m.

The scale of the income - generated through fees to parents - prompted renewed concern over their charitable status with politicians warning that they were "elitist" and therefore failed the test of wider public benefit.