Deputy Prime Minister John Prescott has been admitted to hospital with a suspected chest infection.
John Prescott was taken ill while on a train journey, it is believed
Mr Prescott, 69, is undergoing tests after feeling unwell. His illness is not thought to be life-threatening.
A statement from Mr Prescott's office said: "He has been admitted to hospital. He is undergoing tests as a result of a suspected chest infection."
In May Mr Prescott announced he would step down as Labour's deputy leader and the contest to replace him continues.
It is understood Mr Prescott was taken ill travelling on the train between his constituency in Hull and King's Cross station in London.
Mr Prescott celebrated his 69th birthday on Thursday and recently visited Jamaica and Barbados during a tour of America and the Caribbean.
He is due to leave office on 27 June, at the same time as Prime Minister Tony Blair.
On Christmas Day 2006 he was admitted to Castlehill hospital in Hull suffering from a kidney stone, and released the same day.
Afterwards he thanked the medical staff who had treated him, and added: "They do such a brilliant job, 365 days a year, and it was a real pleasure to have my Christmas dinner amongst such dedicated people.
"What would we do without our wonderful NHS?"
In 2002 it was announced he had suffered Type 2 diabetes for a number of years, managing the condition with medication.