Gassing badgers is the most humane way to control them, according to the Princess Royal.

The royal's intervention emerged after Environment Secretary Owen Paterson announced controversial pilot badger culls will continue this year although will not be rolled out to other areas.

An independent report on the pilots found the level of culling needed to bring about a reduction in TB in cattle could not be achieved by "controlled shooting" - the shooting of free-running badgers.

Mr Paterson noted last year gassing badgers was being considered but would only be used if proven to be safe, humane and effective.

In an interview to be broadcast on the BBC's Countryfile, and quoted on BBC Radio 4's Today programme, the Princess Royal said: "If we want to control badgers, the most humane way of doing it is to gas them."

Dr Rosie Woodroffe, from the Zoological Society of London, said gassing badgers was government policy in the 1970s, adding to the BBC: "If you go back to reports at the time they are full of frustration about how it just wasn't very effective.

"Setts would be gassed and then opened up again by the badgers again and again and again, and the problem seemed to be that badger setts are built to hold warm air in and keep cold draughts out so it's very difficult to achieve lethal concentrations of gas and some lethal concentrations of gas are inhumane. That's why ministers banned gassing in 1982."

She added: "It's tempting to think it might be easier to kill badgers when they're basically a sitting target underground but it turns out from reports done in the '70s that it's not just that straightforward."

In a statement to the House of Commons yesterday, Mr Paterson added measures to tackle TB in livestock in England, cattle movement controls and a grant-funded scheme for badger vaccination projects in areas around the edge of disease hotspots.