Global Radio has responded to a request from Culture Secretary Jeremy Hunt that its £70m acquisition of Guardian Radio Group be investigated by Ofcom.
Hunt has asked Ofcom to investigate whether the deal is in the public interest over concerns that it will give Global control of 20% of the UK radio market. Rivals have argued that the move would also mean Global would own more than 50% of total commercial radio revenues.
"On the basis of the information available to me, I have decided that under all the circumstances and, in particular the concentration of ownership which will occur in some parts of the UK, the merger may be relevant to the issue of plurality, particularly in those areas," said Hunt.
"Accordingly, I consider it appropriate to issue an intervention notice in this case, and I am therefore asking Ofcom to prepare a report advising me in greater detail about plurality."
Assets included in the £70m package include GMG's flagship stations Real and Smooth.
As Ofcom will investigates the deal, the Office of Fair Trading will advise Hunt on competition aspects of the deal.
Both watchdogs will submit their reports to the Department for Culture, Media and Sport by September 28.
If Ofcom concludes that the deal is not in the public interest, Global could be forced to sell parts of the business or even agree to use a certain proportion of airtime for public service broadcasting.
"Global note, with interest, that the Secretary of State has asked Ofcom and the OFT for submissions on a public interest intervention following the recent acquisition of GMG Radio," a spokesperson told Music Week.
"We have already submitted a detailed paper articulating our views and opinions on this subject to the relevant authorities."
In addition to its buyout of GMG radio in June, Global swooped for South-West local station Atlantic FM in May, rebranding it under its Heart banner.