While it has long been the NUT’s official policy that a single union for all teachers would best represent the profession, this has rarely seemed to be a realistic prospect.

Even after the big beasts within the union movement - the NUT and the NASUWT - formed a “historic partnership” in 2012, it didn’t take long for the formal relationship between the traditional rivals to break down over a difference in industrial strategy.

Now it appears that the moderate ATL, left out in the cold by the two other unions’ ill-fated dalliance, now appears to be the most realistic long-term partner for the NUT.

Both unions took part in a conference on professional unity last year; a joint conference on the future of the education sector will take place in June.

This weekend, ATL’s deputy general secretary Peter Pendle took the unusual step of addressing the NUT’s annual conference in Harrogate, stressing his desire for a “closer” relationship between the unions.

“Michael Gove has brought the profession together like no-one else,” he told delegates, adding: “There is so much more that unites this profession than divides us.” Mr Pendle was made welcome by his hosts, with delegates giving him a warm ovation.

He later joined his opposite number at the NUT, Kevin Courtney, for a professional unity fringe. His statement that “with one teacher union, we’d be so powerful we would rarely need to strike” did little to stop tongues wagging that a formal partnership could finally be on the cards.

A motion due to be debated behind closed doors this morning argued that “building a new union for the 21st century” was a “crucial question” for the profession. An amendment to the motion argued that a “secret postal ballot of all members” should take place once the “best possible” merger proposals had been drawn up, suggesting significant progress had taken place behind the scenes.

John Dixon, the NUT’s assistant general secretary, told TES that the union was “very pleased” to be working closely with ATL, and was looking forward to the joint conference in June.

“The policy we have is to work towards a single teaching union, and we have an open invitation to anyone who wants to talk to us about that,” he added.

TES understands, however, that no formal agreement over the creation of a new larger union to replace the NUT and ATL has yet been finalised.

But, with Harrogate’s spring flowers in bloom as the NUT conference draws to an end tomorrow, an inter-union romance could well be on the cards.

A statement from NUT general secretary Christine Blower this afternoon said: “Although there are no formal talks taking place with any teachers’ union at the moment, we continue to be prepared to engage with any union who seeks such discussions.”

ATL general secretary Mary Bousted also said that no formal merger talks were taking place. “We’ve been working with the NUT, among other unions, on issues which matter most to our members especially in the run-up to the general election,” she added.