A union has warned pub managers to “be very afraid” after Birmingham pub group Mitchells & Butlers decided to sell more than 300 of its bars to a private equity firm.

M&B announced on August 20 it would be selling 333 pubs for £373 million to the Stonegate Pub Company, an organisation owned by the TDR Capital private equity house. The deal is set to be completed by mid-November.

But the GMB union said it was worried that the people behind TDR Capital were the same investors behind the financial engineering at Punch Taverns – which has been accused of putting unfair pressure on its licensees through the beer tie after finding itself in financial difficulty.

Hayley Brennan, a lead organiser at the GMB and a Punch Taverns tenant, said: “Here we go again – up hill and down dale with these two who enriched themselves at the expense of our members in Punch Taverns.

“As a Punch Taverns tenant paying a dry rent over three times what the Valuation Office Agency assess as the open market rent for my pub on top of the wet rent I say to staff in these 333 pubs “be afraid – be very afraid.”

The M&B estate being sold comprises 52 Scream bars, 71 music bars, 75 unbranded town centre pubs, 67 drinks-led community pubs and 68 smaller outlets.

The Fleet Street firm, one of the biggest companies in Birmingham, is looking to improve its margins by focusing on food-led pubs, and getting rid of non-core businesses.

Earlier this month it sold its Hollywood Bowl ten-pin bowling business to rival AMF Bowling for £39 million.