An in-depth probe by the Competition and Markets Authority warns that in these areas the takeover of  Birmingham-based HAS-Vent by Swedish giant Landab could lead to reduced choice and higher prices in the construction, particularly for specialist installers of ventilation systems in those areas.

Kirstin Baker, chair of the CMA independent inquiry group, said: “We’re concerned this would remove one of two main suppliers of circular ventilation ducts and fittings in the Nottingham and Stoke areas, risking installers of these systems paying over the odds and then having to pass these costs onto their own customers.

“Our findings are provisional, and we now welcome responses on our preliminary conclusions and the potential remedies in this case.”

In its more in-depth Phase 2 inquiry, CMA officials probed in more detail the impact of the deal on the supply of circular ducts and fittings in England and Wales.

It scrutinised a wide range of evidence, including the suppliers’ internal documents and evidence from installers of ventilation systems and other suppliers of circular ducts and fittings.

The CMA has given Lindab until 12 September to respond to the findings, including submitting any proposals for divesting businesses.