The private equity firm buying defence company Cobham has given legally binding guarantees it will protect British jobs after the £4bn deal goes through.

US business Advent made the pledge as part of its efforts to secure ministerial approval for the takeover, which has now been waved through by Business Secretary Andrea Leadsom.

The sale has sparked fears it could put UK national security at risk because of Cobham’s sensitive military contracts, as well as erode Britain’s industrial base. Campaigners are also concerned at revelations that Cobham will be loaded up with £1bn of debt.

However, regulatory documents filed on Monday revealed Advent has given binding undertakings to ease concerns and get the sale over the line.

Pledges included the new owner keeping UK employee levels at 90pc of the number on the date the sale goes through for five years.

Cobham has about 1,700 UK staff out of a global headcount of around 10,000. Advent has previously said there will be minor cutbacks in back office roles.