Ruth Kelly is the worst Education Secretary since Labour came to power and is not up to the job, a teachers' union leader said yesterday.

Hilary Bills, the new president of the National Union of Teachers (NUT), accused Ms Kelly of patronising teachers and told her to stop interfering in their work.

Ms Kelly, the youngest woman in the Cabinet, may be intelligent but she lacks the "interpersonal skills" required for the job of Education Secretary, Mrs Bills said.

Speaking as the NUT annual conference opened in Gateshead, Mrs Bills said: "I don't dispute that Ruth Kelly is probably an extremely intelligent woman.

"I don't doubt that she has got skills - but not for this job. She is a huge disappointment."

Mrs Bills ranked Ms Kelly, who was promoted to the Cabinet in December last year, behind David Blunkett, Estelle Morris and her immediate predecessor Charles Clarke.

"You may not have agreed with him, but Charles Clarke was somebody you could do business with, you felt that he knew the issues and he understood them," she said.

"Ruth Kelly does not come over as being well briefed.

"The whole way she talks is with that patronising attitude that 'I know better."'

Mrs Bills condemned Ms Kelly's decision to reject proposals put forward by former chief inspector of schools Sir Mike Tomlinson for replacing A-levels and GCSEs with a new diploma.

Mrs Bills said this diploma plan won huge support among teachers but "our views were just swept aside".

And Labour's pre-election promise to put "parent power" at the heart of the party's education policies was also "patronising".

Schools had been consulting closely with parents for decades, said Mrs Bills, headteacher at a primary school in Sandwell, West Midlands.

Mrs Bills's remarks followed angry scenes at the Secondary Heads Association annual conference in Brighton three weeks ago when headteachers jeered Ms Kelly.

NUT general secretary Steve Sinnott later distanced himself from Mrs Bills's remarks.

He said: "The words are those of Hilary Bills. The views of the NUT will be determined over a longer period of time than just a few weeks.

"Ruth's contribution will be assessed at a later stage."

* Mr Sinnott warned that schools could still be hit by a series of teachers' strikes over changes to their pensions and working conditions.

The NUT halted its ballot for industrial action over plans to raise the normal pension age after ministers opened the door for talks.

But Mr Sinnott said he would restart the ballot if ministers failed to honour their promises.