Princess Anne has claimed gassing badgers would be the best way to cull the population of the animals blamed for spreading tuberculosis.

Princess Anne, who is famous for her frank opinions told the BBC: "If we want to control badgers, the most humane way of doing it is to gas them."

The Queen's sister made the comment during what has been called "a frank and forthright" interview on the Countryfile TV show.

The advice however, could put police officers who guard the Royals in an awkward position - because gassing badgers is against the law.

The practice of using cyanide has been outlawed since 1982 and is not an effective way of keeping down badger numbers, according to one expert.

Using gas to cull badgers was also banned because it was found to be inhumane to the woodland creatures.

"It is tempting to think it would be easier to kill badgers when they are a sitting target under ground, but it turns out from reports from the 70s that it is just not that straightforward," Professor Rosie Woodroffe told the Today Show on BBC Radio 4.

"Gassing badgers was government policy in the 70s and if you go back to reports of the time, there was frustration about how it just wasn't very effective. Sets would be gassed and then opened up again by badgers again and again."

Princess Anne's intervention came the day after Environment Secretary Owen Patterson warned that failing to curb tuberculosis could cost up to £1bn. He told parliament: "If we do not control TB, the bill will rise to £1bn over the next decade. It is vital that farmers, vets, non-government organisations and politicians work together to free England of TB."