By Rhys Jones
LONDON, Jan 20 (Reuters) - London's Heathrow Airport was hit by a third straight day of delays on Sunday after airport bosses cancelled 20 percent of flights as snow continued to blanket the British capital, with more forecast.
Heathrow Ltd, which is owned by Spain's Ferrovial , said the reduced schedule - amounting to around 250 fewer flights - would help it cope with the expected snowfall without making further cancellations.
"There is a high probability of around two to six centimetres of accumulating snow and low visibility at periods throughout the day," a Heathrow spokesman said.
"This will reduce the capacity of the airport and without action would cause significant disruption to passengers and flights."
London's smaller Stansted and Gatwick airports said they were operating as normal on Sunday morning but that delays and some flight cancellations were likely.
Weather forecaster the Met Office said snow was likely to continue throughout Sunday and into Monday. As much as eight centimetres was expected in southeast England on Sunday, it said.
On average, some 1,300 flights leave Heathrow daily. The airport, Europe's busiest, operates at close to full capacity after Britain's coalition government blocked development of a third runway in 2010.
Heathrow has spent 36 million pounds ($57 million) on upgrading its winter weather equipment since 2010 - a year that saw it face heavy criticism after it almost shut down when snow hit just before Christmas. It now has 130 snow-clearing vehicles.
More than 400 flights were cancelled on Friday, while on Saturday 111 flights, most of them operated by IAG's British Airways, were cancelled and hundreds of passengers spent the night in Heathrow's terminals.
BA said there had been a knock-on effect because many of its planes were in the wrong place after Friday's snow.
"Like other airlines at Heathrow we have complied with a request to reduce our schedule by 20 percent on Sunday and we continue to work with Heathrow Airport to help keep the airport running as smoothly as possible," BA said in a statement.
"We are doing everything we can to help customers whose flights have been disrupted by severe weather."
Services by Air France-KLM, Ireland's Aer Lingus and Germany's Lufthansa have also been affected.