More than 400 angry parents have signed petitions against Brent’s last non-faith single sex school teaching mixed classes from this September.

Parents claim they were not told that the Crest Boys’ and Girls’ Academy in Crest Road, Neasden, became a mixed school by law last September

They formed a campaign group SaveCrestAC, after discovering in June that boys and girls would be taught together.

One parent who did not wish to be named for fear of reprisal, said: “They registered the school as mixed last year and never told the parents. They consulted parents to merge the school for admin purposes but gave commitment single gender education would continue.

“Lots of parents chose this school not due to its performance but due to preference of single gender education.”

The Crest schools were placed under special measures by Ofsted in 2013, and again this year.

Parents were also upset by promises made under the previous principal Phil Hearne, who was replaced by Mohsen Ojja in January.

He wrote in a newsletter following last year’s consultation: “Lots of parents have asked me whether the merger means the end of single-sex education at Crest. I want to be very clear with everyone within the Crest family: no, it does not.”

Mr Ojja told the Times: “The problem is that with the educational outcomes that there are with the provision being inadequate, we can’t justify remaining single sex education just on the basis of parent choice although I totally emphasise with the parents and I understand their position but being confident and having spoken to them, all they are interested in is the quality of the provision.”

Marina Hashmi, 17, a 6th form pupil with two younger sisters at Crest said her father had concerns. “My sister isn’t comfortable with it either, it’s a big change for her, but I think Crest will get better. The school is doing it for a good reason.”

In 2011 Brent Council defended Crests’ single sex status, writing that the schools “fulfil a need and demand for single sex non denomination [I] education.”

Cllr Ahmad Shahzad, councillor for Mapesbury, said: “My constituents were not given a proper consultation. They were not consulted properly and it wasn’t clear. This school was a single sex school. I can’t get my head around why the previous principle accepted the parents wishes if he knew it was becoming mixed. I urge the new head to listen to the parents, why create friction?”

However Ruth Moher, Brent Council’s lead member for children and young people said: “While I recognise the concerns that some parents have expressed about the school becoming coeducational I support the decision of the principal and governors.

“Crest Academies already has a mixed sixth form and recently has started shared assemblies between the boys and girls in the lower school. The recent consultation also showed that most of the parents who responded were in favour of coeducation.

She added: “Crest Academies are at the moment undersubscribed partly because of the single sex education currently offered. I believe that the vast majority of parents want mixed education for their children.”

A spokeswoman for E-Act, the school’s sponsors said: “Based on the findings presented, and the assurances provided regarding the induction and ongoing monitoring and evaluation, the local governing body, in conjunction with E-ACT as the Academy Sponsor, approved the proposal that The Crest Academies provide a co-education provision from September 2015.”