The 90-year tradition of Scout Jamborees in the UK is under threat because of new Government vetting rules.

As the first phase of the controversial anti-paedophile scheme starts, the Scout Association has warned it could mean major gatherings of packs from around the world are cancelled.

Organising criminal record and other checks on thousands of foreign Scout leaders was "just not possible", a spokesman said.

Volunteers who fail to register face the prospect of criminal prosecution and a fine of up to £5,000.

Simon Carter, Scout Association spokesman, said: "When we hold big international jamborees we rely on adults from other parts of the world coming in and staffing these events.

"The rules for checking people out suggest that if they were to come along and do intensive activity they would have to be checked.

"Clearly we cannot do that, it's just not possible."

The association has written to Children's Secretary Ed Balls asking him to allow voluntary groups greater flexibility within the rules of the scheme.

As well as concerns about major events, it warned parents who wanted to try out volunteering with their son or daughter's pack could be deterred by "bureaucratic and difficult" procedures.

Mr Carter said adults who were supervised constantly while in contact with children should be exempted from the rules for a short period of time.