Five-year-old Isla Stanton walks around the banks of Bewl Water Reservoir near Lamberhurst, Kent.

Wales should sell access to its water "like oil", one former head of Welsh Water (Dwy Cymru) has said.

As southern England suffers under the worst drought since 1976, John Elfed Jones, who is a former chairman and CEO of the company, said Wales should exploit its natural resources as much as it can.

He told the BBC's Taro Naw programme, set to be broadcast on Tuesday, that Wales had to make a stand for "fairness".

"What is fairness? Is it fair that Wales isn't profiting a penny from the water which is exported to England?," he asked.

Around 20m people in south England are affected by the hosepipe ban which came into force last week, including those who get their water from Southern Water, South East Water, Sutton and East Surrey, Thames Water, Anglian Water, Veolia Central and Veolia South East.

Jones said that following one of the driest two-year periods on record Wales should expect the value of fresh water to rise.

"In 50 years will our people look back and ask why didn't we invest years ago?" he said. "It's about time we took this option seriously."

Severn Trent announced on Monday that it planned to sell more than 30m litres of water a day from the region to the east of England.

A spokeswoman for Severn Trent said: “We had to check to see if we had enough water for our own customers. And we are now in a position where we think we can spare the water.”

The plan would see Severn Trent tapping water beneath Birmingham and flowing it into the River Trent, from where it would flow to Lincolnshire and be taken up by Anglian Water.

The company is in talks with the Environment Agency but hopes to put the plan into operation by June. It will charge for the operation, but mainly to cover its own costs.

However Welsh Water says that it is not planning to transfer water to the South East because it is "too expensive and it would not be a practical option either for environmental reasons".