A small number of farmers are turning to knackermen to cull pigs that have backed up on farms. The farmers told the NPA that they could not bear to euthanize their pigs and did not want to ask their staff to do it.

The organization warns that with some farmers getting pigs rolled at a rate of 25-30% per week and contingency plans exhausted, industry pressure will build, resulting in a widespread welfare cull.

NPA chief executive Zoe Davies said: "We know of a handful of farmers who have had to cull some pigs - around 600 we are aware of in total.

"There has been no mass culling yet – although I do believe this is the next stage in the process. As you can imagine this is hugely difficult for the farmers involved and to date none are willing to speak to the press about it."

NPA chairman Rob Mutimer added: “There are now producers actively euthanizing piglets - they have run out of room. They are tending to euthanize the younger ones and get the older ones away as they can.”

Processors have stressed that they are operating at the maximum capacity that staff numbers allow and, in some cases, they have taken steps to ease the backlog by putting on extra kills, albeit delivering lower returns to producers in order to keep things moving.

Despite this, the situation is not markedly improving Mr Mutimer said, and is much worse in some supply chains than others and on some farms than others. Mr Mutimer stressed that things need to improve rapidly before the next pinch point.