A cow added to train passengers' misery today when it wandered on to the line.

Commuters, who have been faced with long delays caused by tracks buckling in the heatwave, were held up until the animal moved from the track near Falmer station.

A spokesman for South Central Trains said a driver saw the cow at about 8.30am. It was later led to safety by a farmer.

There were more problems yesterday when passengers were delayed up to 40 minutes when a track buckled between Burgess Hill and Wivesfield.

The line was fixed shortly after 4pm but passengers on the 14.17 Victoria to Eastbourne service suffered long delays compounded by a 20mph train limit.

Andrew Dobson, 44, who lives at Chailey, near Lewes, escaped a mass scrum at Haywards Heath as people crowded on to replacement buses.

He said: "Luckily I get off here so I avoided the problems caused by the line closure.

"But it was a shambles as everyone tried to get on one of the buses. It's generally been a very painful experience over the last couple of weeks."

Mike Kennedy, 53, of Bluebell Way, Burgess Hill, who travels to work in London every day, said he was getting used to the delays.

He said: "Going home I'm always delayed about half an hour. We are trapped on stuffy carriages and the windows sometimes aren't open. They can get red hot."

Raj Pandya, 36, who also works in London, said: "The trains are often running extremely late and the train operators don't say why.

"It makes it worse because they are often overcrowded."

Tim Nicholson, chair of the Rail Passengers Committee, said: "The problem is getting worse.

"Commuters are obviously getting very angry about it."

Steven Gauge, of Sussex Enterprise, said the rail network was a farce that was damaging business in Sussex.

He said: "We have had the wrong kind of leaves, the wrong kind of snow and now the wrong kind of heat."

Network Rail said there was nothing it could do about problems it blamed on "extreme" temperatures.

A spokeswoman said: "Our tracks are engineered to withstand very cold temperatures, down to minus ten degrees in winter and what we would expect to be a seasonal norm in summer."

South Central said it would continue to operate a 60mph limit while there was a risk of derailment.