Schoolchildren armed with signs and T-shirts emblazoned with protest slogans staged an impromptu demonstration against luxury flats plans to highlight the threat to a so-called “king among trees”.

Pupils at Heathside Preparatory School, next to a derelict nurses’ hostel in New End, Hampstead that is at risk from demolition, gathered on Saturday to rally against plans to build 17 high-end homes and a triple-depth basement car-park.

They joined their parents and teachers to issue the warning “Don’t rock our foundations!” and raise concerns that the plans could damage a 40-year-old “magnificent” copper beech tree.

The protest came one day after the end of an eight-day planning inquiry into the decision by Camden Council to refuse the flats proposals in November 2013.

Barrister Mary Cook, who spoke at the hearing on Thursday on behalf of the dozens of residents opposed to the scheme, described the beech as “a king among trees”. She said: “Far too little attention was paid to trees at the outset.”

Opponents object to the “enormous” size of the basement excavation, which they claim could damage the old beech tree and its roots.

They are also concerned that too many healthy trees would be removed if plans were approved by the Planning Inspectorate.

The copper beech is protected under law from damage or destruction.

Ms Cook added: “The need for car parking alone does not warrant the extent of the basement.”

Barrister Russell Harris QC, for Karawana Holdings, disregarded the concerns, and said many of the trees up for removal would be replaced.

Parents living near to the proposed redevelopment showed the strength of their objections as several brought their children to attend the last days of the inquiry.

Their main concern is for the safety of children at three nearby primary schools, Heathside, New End and Christ Church.

They worry that a child could be seriously hurt by one of the delivery trucks which would drive in and out of New End every 11 minutes if plans were approved.

Mother-of-two Michaela Flanagan, who brought seven-year-old daughter Nancy to the hearing last Thursday, said: “There’s a lot of children in this area and, more often than not, they’re on scooters, so that’s quite concerning because they come whizzing down the hill.”

The 37-year-old Hampstead mother added: “A child going under a lorry, that’s the main concern for me.

‘‘That, and the noise and the chaos that it is going to cause, because it is going to go on for a few years.”