Estelle Morris this week used her first speech on education for two years to criticise the “bigamous” relationships headteachers are forced to have with other schools.

The former education secretary told the National College for School Leadership that too much teacher time was wasted in multi-school projects without proper evaluation of their results.

“If I was a teacher I would quake in my shoes when anyone mentions partnerships. The place is full of partnerships,” she said.

“It is like being a bigamist, to tell the truth. We have entered into so many partnerships in the past 10 years that really somebody ought to call you to account for it.”

In her first major speech on schools since quitting the Department for Education and Skills in 2002, Ms Morris also seemed to contradict the Government’s line on its five-year education plan.

She said partnerships between schools would only really work if extra money was available and that it should be shared among alliances of schools rather than going to only one.

In his blueprint for education, Charles Clarke, the Education Secretary, said high-performing specialist schools should lead “foundation partnerships”, but he has so far failed to commit any cash.

Ms Morris’s comments follow increasing criticism by headteachers of the number of cross-school initiatives introduced by Labour. There are fears teachers are spending too much time away from their own pupils, taking part in federation programmes, Excellence in Cities projects and fulfilling leading edge status commitments.

Ms Morris told headteachers that partnerships between successful schools and struggling neighbours were vital to bridge the class divide which is still hampering academic success.

But she said they should be limited to “harder edge” projects, such as sharing staff, joint budgets and appointing successful teachers as executive heads of more than one school. Speaking at the college’s second annual leadership lecture, she added: “Partnership is crucial but we don’t talk enough about it. We don’t validate it properly. We don’t find the best way to form partnerships.”

Ms Morris helped to oversee the construction of the college - dubbed the “Sandhurst for sirs” - but quit the Cabinet a day before its pound;28m headquarters were due to open.

She made a return to front-line politics last year as arts minister but has already announced she will leave Parliament at the next general election.

Ms Morris has since been tipped as a possible future leader of the leadership college when Heather Du Quesnay, the current chief executive, joins the Hong Kong-based English Schools Foundation in January. This week she refused to discuss the vacancy, saying she was “still thinking” about her future.

In her speech to the college, Ms Morris praised Mr Clarke and said that she had intentionally shied away from education issues. “I have, over the past two years, deliberately decided not to talk about education,” she said.

“This is the first lecture when I have not promoted government policy. I am learning to be a free thinker.”