Defence company Cobham is to be loaded up with debt after a controversial £4bn takeover by US private equity firm Advent.

The 85-year-old British pioneer of air-to-air refuelling is expected to issue more than £1bn of bonds following the deal, which was waved through late on Friday night by Andrea Leadsom, the Business Secretary, in the face of a furious backlash from its founding family.

Advent is funding the takeover with £1.2bn of its own money and using short-term loans arranged with banks including Credit Suisse, Citigroup and Goldman Sachs for the remainder.

It is thought that these banks – which are receiving fees totalling more than £120m for funding the deal – are also being lined up to arrange the bonds, further boosting their earnings from the acquisition.

The debt raise sparked fresh concern from critics of the deal including Lady Nadine Cobham, the widow of founder Sir Alan Cobham’s son. She has previously warned the deal would put national security at risk.

Cobham has about 10,000 staff worldwide, with a fifth of them in the UK. Mrs Leadsom launched a review of the takeover in September but did not make a final decision until after this month’s election.