The test could have approval from the World Organisation for Animal Health and the vaccine could be licensed for UK use by the end of the year.
European Union approval for vaccination would still be required. But a reliable DIVA test would overcome the main objection and discussions in progress, on a comprehensive new animal health law, offer opportunities to negotiate.
The quickest way to a final green light will probably be via that law and nobody can yet put a likely completion date on it.
But to have the UK ready to go with a new policy would be a significant development.
Progress was revealed in a letter from a Defra official to Rethink BTB, a campaign against the expensive policy of culling TB out of the cattle herd.
Rethink BTB published the letter this week, after the Welsh Government abandoned plans to cull badgers, which carry the bovine strain of TB.
Instead, the Welsh environment department will carry out the biggest experiment yet in badger vaccination.
The decision delighted the pro-badger lobby and dismayed farmers, who say both culling and vaccination are necessary.
But Rethink BTB commented: “The main issue has again been missed.
“Any long-term solution must include cattle vaccination.”
Campaign spokesman Michael Ritchie pointed out that the Defra letter referred to evidence, from abroad, that vaccination could prevent between 56 per cent and 68 per cent of TB in cattle – which “vastly outperforms any other measure”, he said.
The Welsh Assembly was on the brink of starting a badger cull last summer but its TB control strategy was taken back for review at the last minute, after Labour gained control from Plaid Cymru.
Welsh Environment Minister John Griffiths announced on Tuesday that he had come to a decision “based on science”.
He said: “I have considered the evidence on potential benefit that might be obtained by vaccination or culling.
“At present, I am not satisfied that a cull of badgers would be necessary to bring about a substantial reduction in cases of TB in cattle.”
Instead, he said, he had asked his chief vet to design a five-year vaccination programme among other measures “towards the ultimate goal of a TB-free Wales”.
The Badger Trust, which fought the Welsh cull plan all the way and promises to do the same with England’s, said: “The Welsh Government has made the right decision. Badger Trust now calls on Caroline Spelman to reconsider her costly, counterproductive cull plans for England.”
If the Trust gets a judicial review of Mrs Spelman’s decision, it will probably try to introduce the Welsh decision as evidence that she is being unreasonable.
But the main farmers’ organisations all say the Welsh minister has made a big mistake.
Joanne Pugh, assistant director of the National Beef Association, said: “We share the disappointment of Welsh farmers. We have huge concerns about the effectiveness of vaccinating sick badgers who are already carrying and spreading TB.
“The only consolation is that the English pilot will show a cull is an effective and essential tool.”