Herb Kohler, the American plumbing magnate who owns the Old Course Hotel and Duke's course at St Andrews, has so far ploughed £39million into developing adjacent Hamilton Hall into luxury apartments, latest accounts reveal.

The Old Course Ltd reduced trading losses last year as the first £1m-plus apartments were sold, and took on an extra 46 staff in response to higher occupancy levels. It also recognised an accelerated £4.6m liability for the wearing out of the tees and greens on the Duke's course. That pushed it to a £5.1m pre-tax loss, and took the cumulative deficit on the profit and loss account to £15.7m.

Mr Kohler, who bought the resort 10 years ago, says the return of the Open Championship to St Andrews next year "will provide a further opportunity to grow revenue and gain more exposure ein the market-place". His corporation also owns the Whistling Straits links, used for US PGA championships, in its home state of Wisconsin.

Hamilton Hall, the former Hamilton Grand seven-story hotel, situated next to the Royal & Ancient clubhouse and overlooking golf's most famous course, was bought at auction five years ago when Mr Kohler was said to be ready to invest £15m in turning it into 26 apartments. They went on sale in July 2013 at prices from £1.3m to £7.6m, and 13 had been sold by March this year. Owners enjoy a members' library and grill restaurant, a roof garden, valet parking, a 24-hour concierge, and a bar open to the public.

Writing in the accounts, Mr Kohler says the 24 per cent increase in turnover, up from £12.8m to £15.9m, was largely due to the first apartment sales, though benefited from an increase of 8.1percentage points in the occupancy rate. The £3m turnover hike translated into a £1m improvement in profitability, the underlying loss reducing from £1.46m to £439,245.

Mr Kohler said: "The increase in occupancy rates was offset by investment in refurbishment work, sales and marketing activities and salaries and wages to service the increased occupancy levels at the industry's highest standards."

The accounts show employee numbers rising over the year from 299 to 345, with the addition of 41 operating staff and five in administration. The headcount has now increased by 28 per cent in the past two years.

Underlying administrative costs were up from £3m to £3.2m, with the pre-tax loss of £5.1m more than three times the £1.6m of 2012, due to the accelerated depreciation of the Duke's course, which is being depreciated over 15 years.

The fixed assets are shown at a total cost of £64.7m with accumulated depreciation of £28.2, giving a net book value of £36.5m, down from £40.7m.

The Old Course Ltd, which includes former R & A secretary Sir Michael Bonallack among its directors, has a loan from the Kohler group of £63m, a rise from the previous year's £57m, with no repayment date. Shareholder funds however are down from £13m to £7.9m.

On Hamilton Hall, Mr Kohler says the delivery of the development in terms of construction costs and unit realisations will extend over a number of years, hence the costs are categorised under 'stocks' in the accounts. Development work in progress is shown as rising from £27.6m to £33.9m, but that figure is also shown as a net cost after a provision of £4.9ml the same as the previous year, suggesting a total investment to date of some £39m.

Mr Kohler writes: "Competitive pressure in the UK and international resort markets are continuing risks for the company, particularly against the backdrop of the current economic climate. The company manages these risks by investing in superior quality products and services in an effort to distinguish itself from its competitors."