London mayor hopeful Ken Livingstone has challenged the government to fulfil its promise to find time for his backbench bill to outlaw hunting with hounds.

Unveiling his private member's bill, the keen animal breeder revealed a fox had once bit the head off a tortoise he kept in his garden.

But he insisted he was not a "sentimentalist" and understood foxes had to be controlled.

"I have witnessed the cruelty of nature," he said. "What there can be no excuse for is the unnecessary cruelty of hunting with hounds."

The Labour MP acknowledged no progress could be made with his bill, the fourth attempt to ban fox hunting in seven years, until Lord Burns had completed his inquiry into the effects of such a move on rural unemployment.

He said he then expected Home Secretary Jack Straw to keep his promise to find time for a hunt ban bill before the end of the parliamentary year in November.

"I will go out of my way to co-operate with the government in any way I can to make sure we honour this commitment to Labour voters," the rebel MP said.

His bill, which was published and received its first reading on Wednesday, is a near replica of one brought by Michael Foster, which failed due to lack of parliamentary time despite the support of 411 MPs.

Mr Livingstone denied his decision to bring it had any connection to his campaign to become Labour's candidate for London mayor.

The fact the Burns inquiry will not report until June meant any move on the bill would come "after all the mayoral shenanigans is over", he pointed out.

He rejected questions about what would happen if the Labour Party plumped for Frank Dobson as mayor candidate and he was persuaded to run as an independent, a move he has repeatedly and unconditionally promised never to take.

"It wouldn't matter if I suddenly became a Trappist monk. The bill would still be on the agenda and others would take it forward."

All the hopefuls in the mayor contest, including Tory favourite Steve Norris, agreed fox hunting should be banned, he said.

Mr Livingstone said he had only decided to take the bill forward after fellow Labour MP Tom Pendry opted for a private member's bill to address carers' needs instead of a hunt ban.

Mr Pendry came second in the private members' ballot, while Mr Livingstone only placed eighth. Traditionally, only the top six bills stand a realistic chance of becoming law, but if it receives the extra time Mr Livingstone is demanding a fox hunt ban could become law this parliamentary session.

Mr Pendry later said he had not brought a hunt ban bill because he felt it stood no chance of becoming law.

"By the time the inquiry comes out I would not have been able to get a hunt bill through," he said.

The chairman of the Campaign for the Protection of Hunted Animals, Douglas Batchelor, hailed the move as part of the march of progress.

He said: "In the 19th century, dog fighting, bull baiting and cock fighting were banned and the 20th century has seen dozen of new laws to protect animals from deliberate cruelty or neglect.

"Ken Livingstone's bill now gives us the chance to start the 21st century by ending the equally cruel and outdated sport of hunting wild mammals with dogs."

But the Countryside Alliance argued Mr Livingstone had failed to seize the chance to address a subject close to voters' concerns.

A NOP poll it commissioned found only 8% of those asked choose a hunt ban from a list of possible topics for private members' bills. The first choice was a bill to provide free TV licences for pensioners.