Rock musician Brian May has threatened legal action if the controversial badger cull goes ahead for a third year.

The Queen guitarist said his Save Me Trust planned to challenge the lawfulness of the cull if the two four-year pilot schemes continue in both Somerset and Gloucestershire or is rolled out to new areas.

It is thought that Natural England will soon announce the licensing of a third year of culling in Somerset and Gloucestershire and may extend the pilot to Dorset.

"Lawyers instructed by the Save Me Trust have today written to the chief executive and the chief legal advisor of Natural England warning them that if any licences to cull badgers are either activated in Gloucestershire and Somerset or any new licences granted for this purpose anywhere, then the lawfulness of the decisions to do so will be challenged by a judicial review in the High Court," a Save Me Trust spokesman said.

"To continue the culling of badgers is unlawful as it does not rationally serve the statutory purpose which permits the killing of badgers only to achieve the aim of preventing the spread of disease.

"Additionally there has been a fundamental failure in the consultation process, a logically flawed approach in calculating badger numbers and a failure in Gloucestershire in any event to meet its minimum targets in 2013 and 2014."

In the run-up to the General Election environment secretary Elizabeth Truss vowed to extend the cull to areas where tuberculosis was rife in cattle.

Last year just 274 badgers were culled in the second year of the pilot in Gloucestershire - falling far short of the minimum 615 estimated to be needed to deliver reductions in TB in livestock, and leading the chief vet to admit the benefits of the cull might not be realised there.

The Government claimed the low numbers in Gloucestershire reflected the "challenges of extensive unlawful protest and intimidation" by anti-cull campaigners.

In Somerset, a sufficient number of badgers were killed this year to lead to expected reductions in TB in cattle, with 341 culled, in a required range of 316 to 785.

In both of the pilot areas, a significant proportion were killed by the more expensive cage trapping and shooting method, rather than "controlled shooting" of free-running badgers.

Ministers and farmers insist culling is necessary to tackle TB, which can be spread from badgers to livestock, with more than 26,000 cattle slaughtered in England last year and multimillion-pound losses.

But opponents say badger-culling is inhumane and ineffective, and alternatives such as vaccination should be pursued.

An independent expert panel concluded that controlled shooting of badgers in the first year of the cull was not effective or humane.