Russell Hobby, general secretary of the National Association of Head Teachers, threatens a first strike since the NAHT was established in 1897:
"Unless negotiations produce real results, the NAHT will ballot its members in late September on industrial action over pension cuts.
"If our members vote yes, and they appear definite on the matter, we could see school leaders on strike for the first time since the union was established in 1897. It is a desperate time for our members who instinctively do not want to leave their posts even for a day.
"They believe they are not only defending existing pension rights but trying to protect the future of education in this country. If we do not value teachers, we cannot hope to signal to the best graduates that this is the right career for them."