The Farm Animal Welfare Council, a Government-appointed advisory body, this week refused to comment on a series of reports that it is preparing to condemn the way hens are hung upside down before being stunned in readiness for decapitation.

The reports were all based on comments from a FAWC member at an open day for the press. But the organisation has since discussed its provisional findings with industry stakeholders and nobody has denied the gist – that the investigators agree that "live shackling" causes pain and distress, particularly as selective breeding means many birds have leg and joint problems anyway.

The problem for the industry – and Ministers – is that there is not a proven alternative method of making birds ready for the "electric bath" which stuns them, before their throats are cut.

Withdrawal of approval for the system would probably mean pushing the abbatoirs to equip for another system altogether, such as gassing. That is already common in the turkey business, because the problems of shackling – and getting a reliable stun shock – have already been acknowledged with heavier birds.

Some European countries already favour gassing systems for chickens too. But there are objections to them too and the European Union has been failing to agree on common standards for some years now.

Ministers asked FAWC to look at the UK broiler business two years ago. According to industry sources, the report, due in December, is likely to say that live shackling should be "phased out".

That will leave Ministers to decide whether there is a case for unilaterally imposing a new expense on the UK industry or whether to take the argument back to European and world regulators first.

But animal welfare campaigners are bound to use the FAWC report to put the pressure on – and the various food standards agencies will be pushed into comparing their slaughter policies.

Peter Stevenson, policy advisor of Compassion In World Farming, was at the last FAWC briefing for "stakeholders". He said this week that he could not comment on the discussions which took place but it would be surprising if the FAWC report did not comment on the shackling controversy, because that was one of the reasons it was ordered in the first place.

Mr Stevenson said he had reluctantly come to the conclusion that gassing was the least unacceptable way of dealing with the huge numbers of birds killed for meat – 800 million a year in the UK.

But the British Poultry Council said it believed improvements to the existing system could meet most objections. Experiments are in progress in guiding birds along a conveyor belt to a point where they would be stunned or killed while still standing.

Chief executive Peter Bradnock said: "The needs of small specialist producers must be taken into account and many of them depend on local slaughterhouses which would struggle to re-equip."

He added: "The maximum length of time a bird will be conscious and shackled has been reduced to two minutes and on most premises it would be less than half a minute."