Leading figures in Britain's horse racing industry are threatening to move their animals overseas because of plans for more than 400 aircraft a day to circle over their stud farms.

National Air Traffic Services (Nats) is proposing to create a new holding stack near Newmarket, Suffolk, for aircraft queueing to land at Stansted. The stack is one of two being created to cope with a large expansion of the Essex airport.

Stansted handles about 190,000 flights a year at present. BAA, the Spanish-owned company that runs the airport, wants to increase that number initially to 260,000 on the existing runway and then to open a second runway in 2015, raising total capacity to more than half a million flights a year.

Newmarket, at present one of the most tranquil areas in East Anglia, has the largest concentration of stud farms in Europe. The Derby winners of 2006 and 2007, Sir Percy and Authorized, both retired to stud there, and this year's winner, New Approach, is also likely to end up in the area.

More than 7,000 thoroughbreds are cared for by 2,000 people on stud farms in a few dozen square miles underneath the proposed stack.

A study commissioned by the Newmarket Horse Racing and Breeders Group suggested that almost two thirds of the stud farms would either move or curtail investment in the area because of the noise and air pollution created by the stack.

Aircraft would descend in spirals to 7,000ft (2,100m) before breaking out of the holding pattern to make their approach to Stansted. Some would pass over the stud farms as low as 4,000ft. The group says it has been told by Nats that the noise of an aircraft at 7,000ft is similar to that generated by a van passing within 50ft at 40mph. Another 100 aircraft would pass over Newmarket en route to a stack for Luton airport.

The study found that many of the stud farm owners were international businessmen and women with horseracing interests in other countries, to which they could easily move their Newmarket horses. Dalham Hall, the biggest stud farm in the area, employing 250 people, is owned by Sheikh Mohammed Al Maktoum, the ruler of Dubai. He also keeps and breeds racehorses in Ireland, France, the United States, Australia and Japan.

Newmarket's stud farms and racehorse trainers collectively spend more than £100million a year in the area on wages, goods and services. The study said: “Much of this investment is footloose in the sense that it is capable of being invested in a number of locations in the world, Newmarket - and indeed Britain - being merely one of them. A clear consideration in making such investment is the high quality of the environment around Newmarket and the absence of any pollution. It would not take much for owners to choose other training and stud locations and not to invest here.”

Alastair Watson, chairman of the Newmarket Stud Farmers Association, said: “We realise that the stacks have to go somewhere but we have a hundred employees for every 1,000 acres and they spend 85 per cent of their time outdoors. Elsewhere in East Anglia there is only one person per 1,000 acres and he's sitting in a tractor and wouldn't hear the aircraft.”

Nats claims that the new stacks will result in fewer people overall being exposed to excessive aircraft noise because its guiding principle has been to move flight paths from urban to rural areas. More than 62,000 people live under the two existing stacks shared by Stansted and Luton, compared with 40,000 under the three stacks being proposed to replace them.

But critics of Nats's policy point out that low-flying aircraft will be more noticeable in the countryside because there is less background noise.

A Nats spokesman said that the consultation on the proposals would end on June 19. The new stacks are due to begin in March. He added: “The racing community in Newmarket has made comments and these will be considered after the consultation closes.”

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