Several local authorities bordering an area with selective schools have said they would welcome grammar “annexes” in their areas, leading to questions over Nicky Morgan’s promise not to open the “floodgates” on grammars.

In the run-up to this week’s local elections, Conservative councillors in Milton Keynes, a non-selective local authority, promised grammar annexes if they were elected.

Three more non-selective local authorities, which also border the selective county of Buckinghamshire, say they would also welcome satellite grammars.

In October last year, the education secretary approved plans from the Weald of Kent girls’ grammar in Tonbridge, Kent, to open an annexe nine miles away in Sevenoaks, also in Kent. At the time, she said it would not “open any kind of precedent or floodgate”.

Buckinghamshire has the second highest proportion of pupils in grammar schools in the country – 42 per cent attend one of its 13 selective schools. Many pupils also travel from neighbouring authorities.

Rebecca Hickman, a member of anti-selection campaign group Local Equal Excellent, said: “These proposals for satellite grammar schools are being brought forward at an alarming rate and gives a lie to Nicky Morgan’s claim that the Sevenoaks decision would not ‘open floodgates’.”

In March, the government updated a form for academies wanting to make significant changes to their intake, including adding a tick-box for selective schools that wanted to expand on so-called satellite sites several miles from the school.

Edith Bald, Milton Keynes’s Conservative party leader, said parents wanted a grammar in the town as results were better at grammar schools.

Currently, 1,400 children from Milton Keynes travel at least 15 miles a day to attend one of Buckinghamshire’s four grammars in Buckingham or Aylesbury.

Bald said: “The main opposition is going to be the heads in Milton Keynes who will say this would cream the talent out of their schools. But any child in Milton Keynes can sit the 11-plus already, and many do, so those children are already leaving.”

But anti-grammar campaigner Hickman said data showed achievement gaps in Buckinghamshire were some of the largest in the country and “middle ability children perform worse than they would in a comprehensive system.

“Champions of selection focus on the good results that grammar schools achieve, but rarely talk about what happens to the 75 per cent of children who are rejected.”

As previously reported by Schools Week, the Royal borough of Windsor and Maidenhead is also looking at whether Sir William Borlase’s grammar should open a satellite site in Maidenhead, five miles from the original school.

Phillip Bicknell, cabinet member for education, said the council was in the “very early stages” of working with the school, but it was “important” parents had “choice”.

Two more non-selective local authorities also bordering Buckinghamshire – Oxfordshire and Hillingdon – said they would support grammar annexes.

Melinda Tilley, Oxfordshire’s education lead, said: “My view is that the more choices we give parents the better.”

David Simmonds, Hillingdon’s cabinet member for education and deputy chair of the Local Government Association, said: “It would be a popular move with parents . . . as many parents already take their children to grammars in neighbouring areas.”

A government source said applications did not signal approval and Morgan’s statement about not opening floodgates or setting a precedent still remained.