A scheme to build 425 new homes in Leavesden could stretch nearby schools to breaking point unless more money is spent providing new classrooms, Hertfordshire County Council has been warned.

A combination of one and two bedroom flats and two to five bedroom houses including 148 affordable homes could be built on the former site of the Rolls-Royce factory at Leavesden Aerodrome.

Outline planning permission for the construction of the homes, shops and a ‘town square’, was granted by Three Rivers District Council in December 2011 and the first of five phases of construction could begin in early 2013, subject to planning permission.

The county council was not able to say how many pupils the development would bring to the area but it is understood to be asking developers Bellway for a contribution of £1.8m towards the cost of providing extra places.

Councillor Stephen Giles-Medhurst, Liberal Democrat county councillor for Central Watford, urged the county council to act quickly to ease the pressure on already crowded schools.

He said: “If the county council hadn’t closed several schools in the area this wouldn’t be such a problem now.

“Less than 10 years ago they tried to close down Leavesden Green, we said they were wrong to do so at the time.

“The county council have known there was a plan to turn this site into a residential development for the past 18 months or so. “It is up to it to put its house in order.

”They now have to come back with some firm proposals because if something isn’t done we will be in an even worse position.”

A public consultation into the development is due to begin later this month and the developer would then be required to apply to Three Rivers District Council for planning permission.

But Councillor Giles-Medhurst warned that lack of school places could not be taken as a reason to block development.

He said: “I think we should be pleased that in the current climate the developers want to push ahead with such an ambitious development.

“This will improve the local economy and will create a number of jobs, at least for a couple of years while construction takes place but hopefully after that too.”

Lesley Folgate, a teacher at nearby Parmiter’s School, said: “There are a lot of children around here and not too many school places.

“I understand they will have to increase form entry at some schools.”

Bellway Homes bought the 38-acre site in March after outline planning permission had previously been secured for the development.

Three Rivers District Council placed a number of demands on the site including a requirement that no residential roads run between Aerodrome Way and South Way, which could be used by commuters as a short cut to the M25.

A large green area to the north known as Horsefield was also signed over to the council by developers to be used as a community space.

Abbots Langley councillor Sara Bedford said: “The developers are just starting to talk with councillors, residents and other interested parties. No decisions have yet been made and we will be insisting on full consultation with everyone affected by the new homes before the plans are taken any further.”

A Hertfordshire County Council spokesman said: “We are implementing the expansion of Tanners Wood Primary School from 45 pupils to 60 pupils on a permanent basis from September 2012 and a temporary increase of 30 pupils at Abbots Langley Primary for one year to meet current demand. “We are monitoring pupil forecasts and will increase school places in line with projections, either through school expansion or new provision in line with our countywide strategy to meet increasing demand.”