The National Union of Teachers (NUT) has been left in a “difficult” position by the NASUWT’s decision not to take part in a joint national strike next month, an education union expert has claimed.

On Friday, the NASUWT confirmed that it would not be going on strike on 26 March alongside the NUT, despite the unions’ recent programme of joint industrial action following their “historic” joint declaration last year.

Since formally joining forces, the unions have conducted an ongoing campaign of action short of strike action and held two regional strikes during the autumn term.

In October, the unions vowed to hold a joint national strike unless Michael Gove agreed to talks to resolve their dispute over pay, pensions and working conditions.

TES understands that, after protracted discussions between the unions’ leaders failed to result in a joint strategy being agreed, the NUT decided to go it alone and announced a national strike on 26 March. NUT general secretary Christine Blower told TES it would have been in the “best interests of the profession” for the NASUWT to be on board.

However the NASUWT will not be taking part, and on Friday claimed this was due to Mr Gove accepting the recommendations of the School Teachers’ Review Body (STRB) - warmly received by the unions - published the previous day, as well as the “belated commitment by the secretary of state” to discuss its trade dispute issues. An “agenda setting meeting” has been scheduled for 25 February.

The NASUWT’s announcement on Friday cited the impact of the “widespread disruption already affecting children, schools and communities as a consequence of the winter floods crisis”, and insisted the talks with Mr Gove offered a “window of opportunity for genuine progress to be made”.

“The NASUWT national executive and NASUWT members recognise that the only way to resolve a dispute is for the parties directly involved to sit down to have serious discussions on the issues of concern,” general secretary Chris Keates added.

On Twitter, some NASUWT expressed frustration with the decision. “I am disappointed in my union’s decision not to strike, but very little support [came] from members during the last one,” wrote @there_runsMary, while @HeyMissSmith said it was a “shame” the unions were “not taking the same stance any more”, adding: “This weakens our argument considerably.”

Howard Stevenson, professor of educational leadership and policy studies at the University of Nottingham, said that he was “not surprised” by the NASUWT’s decision.

“I have never sensed the NASUWT were anything like as enthusiastic about the industrial action as the NUT were, so I am not surprised therefore that the STRB report prompted them not to call immediate strike action.”

The report, which dismissed several proposals by the Department for Education, had “driven a wedge between the unions”, he added.

While insisting that the NUT had so far run a “good campaign” of engaging and mobilising its members which had “tapped into the mood [among teachers] about the current direction of education policy”, Professor Stevenson said that the NASUWT’s decision had left it somewhat isolated.

“It’s very difficult for any one union to prosecute and maintain a dispute on its own. That’s the position the NUT finds itself in.”

He pointed out that an NUT conference on 1 March about the prospect of “professional unity” - creating a single union for teachers, an official policy of the NUT - would not be attended by the NASUWT.

“They are clearly maintaining their long-held position that teachers’ interests are best served by having competing unions,” he said.

“The alliance with the NUT was always for that reason going to be a difficult one to maintain. While there has been a pragmatic alliance between the unions on particular issues, there is little prospect of this turning into a stronger alliance.”