Heathside School has confirmed it will abandon its boarding premises at West Heath Road after protracted discussions and a High Court case with Barnet Council.
In an announcement today, new owner Dukes Education said it would be leaving the site from July 2020 - the end of the current school year.
It comes after months of discussions with the local authority, which had applied to the High Court to force Heathside to leave over an alleged breach of planning consent.
Heathside, which changed hands last July after 27 years of continuous ownership, is split across six different sites in Hampstead and caters for around 500 pupils aged two to 14.
Redundancies are expected as a result of the move and the school is now casting about for new buildings to house its Year 7 to Year 11 pupils in the long term.
A spokesperson said: 'When Dukes Education acquired Heathside School in July 2019, there were a number of significant legacy issues to be dealt with.
'Since July, Dukes have spent a great deal of time and effort in attempts to reach a compromise with Barnet Council that would allow the school to remain at this site with a reasonable cohort of day school pupils.
'Dukes successfully managed to negotiate a temporary stay until July 2020, to allow the school to continue during the current academic year.
'However, despite positive initial meetings, over the recent weeks, it has been made clear that Heathside is unlikely to ever gain the permission that would allow us to operate a viable school there and so it is with regret that Heathside will leave the West Heath Road premises at the end of the summer term and, as a result, we expect to make a number of redundancies among the staff at the High School.'
Dukes, a nationwide schools operator, added that it had the funds in place to acquire a property quickly once an agreement was made, including 'major investment' to bring it up to the expected standards.
It is expected that acquiring a new site will take up to a year. During the transition phase, Dukes said, it would 'reorganise' the school to ensure it could accommodate all its year groups on the existing sites.
Heathside's former parent company, Remus White Limited, collapsed into administration last year owing more than £3million to creditors, including parents.
It came following a staff and pupil exodus over two years, prompted by two highly critical Ofsted reports and a catalogue of safeguarding concerns.
After the acquisition by Dukes Education, announced on the last day of term last year, Ofsted inspectors returned and said the school was now meeting the required standards.
The spokesperson added: 'Heathside Prep school is not directly affected by these changes and our staff there remain fully committed to delivering the first-class education in the special, nurturing environment that makes Heathside so special.
'Our goal, as we face these challenges, is to remove the uncertainty that has hung over our senior school provision and enable us to face the future in a far more secure fashion.'
Barnet Council has been approached for comment.
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