The European Commission’s (EC) investigation into CK Hutchison’s proposed acquisition of Telefonica O2 in the UK centres on four key areas, according to the Financial Times.

A questionnaire sent to companies in the mobile industry covers four main areas; retail competition, sales channels, infrastructure and wholesale services provision.

The commission announced at the end of October it will be running an in-depth inquiry into the takeover which would create the UK’s largest mobile operator.

The EC has become more sceptical about deals which reduce the number of operators in a market from four to three under competition chief Margrethe Vestager.

A large part of the questionnaire contains questions on the impact of the merger on wholesale access to rival providers.

The commission asked respondents to judge what effect a 5 per cent rise in wholesale costs would have, as well as the impact on average retail prices if costs per subscriber fell by 10 per cent.

The questionnaire also asks whether there will remain a sufficient number of providers of passive network infrastructure following any deal.

The commission is also interested about the impact on high street retailers, such as Carphone Warehouse, which act as third-party resellers of mobile services.

Following any takeover, there is a risk that 3 and O2 brands could be withdrawn from stores, weakening independent retailers.

The EC is expected to use the responses it receives to the questionnaire to create a so-called statement of objections in January, which it will present to Hutchison and Telefonica. It has a deadline of 18 April 2016 to reach a final decision.