Conservative HQ was under siege last night after it was accused of a "humiliating U-turn" on the issue of grammar schools in England.

Having provoked the wrath of Tory traditionalists by insisting there would be no increase in the 164 grammar schools south of the border, David Cameron was accused of "caving in" to pressure from within his party's ranks when it emerged there could be circumstances in which the Tory leadership would approve of more grammar schools.

Just 48 hours after Graham Brady resigned his Opposition front-bench post, Dominic Grieve, the Shadow Attorney General, fuelled the row in a local newspaper article.

The MP for Beaconsfield told the Buckinghamshire Examiner that while his party was looking to reform the education system nationally, there was no question of it changing the county's selective education system against local wishes.

However, he added: "We must also ensure if further grammar or secondary schools are needed, they can be supplied within the county."

Tory Central Office confirmed some new grammar schools could be built "on a case-by-case basis, if the demographics required it".

Last month, Mr Cameron declared emphatically that building new grammar schools was "delusional" and "not practical politics" while this week George Osborne, the Shadow Chancellor, said: "While the existing grammar schools are safe with us, we will not promote the opening of new ones."