London: Theresa May is backing a bid to open the first new grammar school in 50 years.

The Home Secretary voiced support for a `satellite’ grammar to be set up in her constituency alongside existing comprehensive schools.

If the new school is pushed through, it would mark the first significant expansion of academic selection since the 1960s Labour government started a campaign to convert the country’s 1,300 grammars into comprehensives.

May’s backing for the project sends a strong signal to others in her party amid speculation over the future Tory leadership.

Laws which ban the creation of new grammars remain in place but the proposed school would be permissible because it would be an annexe under the umbrella of an existing grammar in a neighbouring local authority.

The plan is being developed by the Tory-run Royal Borough of Windsor and Maidenhead, which overlaps with May’s Maidenhead constituency.

While secondary schools in the borough are comprehensive, four neighbouring local authorities — Buckinghamshire, Reading, Slough and Surrey — have grammars.

Windsor and Maidenhead has already made contact with all 17 of the surrounding grammar schools and secured two expressions of interest — from Sir William Borlase’s Grammar in Marlow, Buckinghamshire, and Reading School.

The satellite school, which could open in September 2018 at the earliest, would help meet demand for new secondary places driven by a rising population. The borough has calculated there will be a shortfall of 100 secondary places in Maidenhead by 2020.

It will produce a further report next year on the viability of including a grammar school annexe.

A statement on May’s constituency website said she `welcomed plans to consider the option of a ‘satellite’ grammar school’.

She said: “Grammar schools attract considerable support from Maidenhead families. If a good school wishes to expand in line with existing legislation then this must be seriously considered.”

Some 163 grammar schools remain in England, in 36 out of 150 local education authorities. New admissions rules introduced by former education secretary Michael Gove in February 2012 made it easier for schools to expand in response to parental demand.

This paved the way for grammars to consider operating satellites on separate sites as long as they retain the same staff and admissions policy. However the first attempt to create an annexe — in Sevenoaks, Kent — was vetoed last year.

Sources said at the time the decision was based on the merits of that particular application, rather than opposition to the principle of a grammar satellite.

Concerns included that the proposed Sevenoaks satellite was to be a mixed school while its sponsor was a girls’ grammar.

New satellite grammars must share the same ethos as their `parent’ schools to avoid flouting Labour’s 1998 legislation outlawing new grammars.

Gove’s successor, Nicky Morgan, has signalled she will follow demand when creating school places, saying that “if grammar schools want to expand, we’re not going to stand in their way”.

If the Windsor and Maidenhead plan comes to fruition, more authorities could follow their lead as competition intensifies for grammar places following a baby boom.