That's 'dirty' as in rampant with infected wildlife, which Defra would rather not touch with a very long pole, rather than anything whatsoever to do with cattle.
But having carved the country up into
In another life, and contributing greatly to MAFF staff pensions, many of us joined the voluntary EBL (Enzootic Bovine Leukosis) eradication scheme. The country eventually became EBL free so these schemes were no longer needed, but the way they worked was to issue the farm with a certificate of compliance which accompanied any cattle sold.
The certificate was an official State Veterinary Service document, having the farm name and holding number on the top and then a gap for animal details.. Any animal sold from the farm was accompanied by a copy of this document, and to keep its EBL status, wherever it was, it had to be retested by the date on the paperwork which is this case was three years from it's clear blood test. In effect an MOT for cattle.
So, would this work for TB?
The result of the last TB test is important, but the due date of the next one is crucial.
Rather than divide up historically affected areas, assuming but not really sure that 4 year testing areas are clear of the disease, why not issue an Animal Based Certification of TB testing after a clear test, with the date of the next due test on the paperwork?
This would not penalise or stigmatise any farm unlucky enough to have experienced a breakdown, but would ensure that cattle traded into 4 year testing areas were tested on the consigning farm's regime, at least once. It would also be a reminder to people buying from farms in these so called 'clean' areas, who may be dispersing cattle just before a herd test is due.
The 'due date' could be flexible enough to include the animal at a routine test - within reason. But should farmers not comply with this requirement to test, then if the animal concerned was subsequently found to be a reactor, compensation could be affected.
(Steers due for slaughter could be exempt as abattoir surveillance would pick up any problems. )