Health officials confirmed that a woman died just before 1800 BST on Sunday at Furness General Hospital in Barrow. She was later named as Harriet Low, 74, of Barrow-in-Furness.

An 88-year-old man and two women, aged 54 and 56, have already been killed by the bug since the outbreak in Barrow was identified on 2 August.

Two people in Bedfordshire are also being treated for Legionnaires' disease.

We are by no means through this terrible time for the people of Barrow

Ian Cumming, chief executive, Morecambe Bay Hospitals NHS Trust

One person, from Luton, is recovering in the Luton and Dunstable Hospital.

The three cases are not thought to be linked to the Barrow outbreak.

Chief executive of Morecambe Bay Hospitals NHS Trust, Ian Cumming, sent his "deepest sympathy" to the family of the latest victim.

He added: "The disease is a very serious condition with a high in-hospital mortality rate.

"Furness General Hospital continues to see an improvement in the condition of the majority of the 40 cases remaining in hospital but, as this further death shows, we are by no means through this terrible time for the people of Barrow."

The Cumbria outbreak is thought to have begun at this leisure centre

The outbreak of the pneumonia-like illness in the town is the biggest ever in the UK, with 131 confirmed cases.

The source of the outbreak is believed to have been the council-run Forum 28 Arts Centre in the centre of the coastal town.

Tests on a 30-year-old air conditioning system found traces of the Legionella bacteria, which causes the disease, in the water treatment plant.

A council worker has been suspended.