The change from toothing to a calendar date in the carcase splitting decision for TSE has now been officially delayed and will not take place this season.
Planned changes to carcase splitting rules for lambs born in 2018 onwards will now be be abandoned.
The National Sheep Association (NSA), responding to Defra's confirmation, said it is 'naturally disappointed' in the move.
Farmers have campaigned for over a decade to change the way lambs are aged from dentition checks to a cut-off date, which would improve accuracy and transparency and ensure that farmers are paid fairly for the value of their product.
The NSA said another season must now pass at a cost to the sheep industry that it estimates is in excess of £24m a year.
The body's Chief Executive, Phil Stocker said: “There will be some farmers out there who have bought lambs and fed them with the expectation of the move to the 30th June date, and the only silver lining is that people now know what they are working with for the remainder of this season and any uncertainty is now past.”
The group is now pushing for a timetable to ensure this change is worked on and implemented ahead of the 2020 season.
Mr Stocker adds: “While the change won’t come this season there is no reason why Defra and Food Standards Agency (FSA) should not continue to push forward immediately with the aim of finalising things before the 2019 store lamb sales begin in late summer.
“This isn’t a matter of accepting defeat, we were told this was a Brexit no deal related delay and we now have to push forward within the window available.”