Deputy Prime Minister John Prescott has spent a second night in hospital, with a suspected chest infection.
John Prescott was taken ill on Saturday
Mr Prescott, 69, underwent medical tests after he was admitted on Saturday, but his condition is not understood to be life-threatening.
He has apologised for missing an event marking the 200th anniversary of the British act abolishing the slave trade.
It is believed Mr Prescott was taken ill on a train from his constituency in Hull to London King's Cross.
His office has declined to confirm which hospital he is being treated at.
Mr Prescott had been due to meet young people on Monday from the former slave ports of London, Liverpool and Bristol who will join the crew of a replica 18th century slave ship, the Amistad Freedom Schooner.
From his hospital bed he sent a message apologising for his absence and wishing the venture well.
Mr Prescott celebrated his 69th birthday on Thursday and recently visited Jamaica and Barbados during a tour of America and the Caribbean.
In May Mr Prescott announced he would step down as Labour's deputy leader and the contest to replace him continues.
He is due to leave office on 27 June, at the same time as Prime Minister Tony Blair.
In 2002 it was announced he had suffered Type 2 diabetes for a number of years, managing the condition with medication.