Britain’s communications watchdog has called for an investigation into the dominance of Microsoft and Amazon in the country’s cloud computing market, in the latest challenge to the tech giants from global regulators. From the report. Ofcom said on Wednesday it was “particularly concerned” about the practices of Amazon Web Services and Microsoft, which together control 60 to 70 percent of the UK cloud market. It recommended that the sector be referred to the Competition and Markets Authority for further investigation. Cloud computing is dominated by Amazon and Microsoft and has become an important revenue driver for the tech giants. But growth in demand for these services has slowed this year and customers have sought to cut costs, with some complaining of rising prices and difficulty switching between cloud providers. Ofcom’s move comes amid increasing global scrutiny of the cloud market. Last year, Microsoft changed its cloud licensing policy in Europe in an attempt to fend off potential antitrust action by Brussels regulators. Tech companies are already the targets of US, UK and EU competition controls on several fronts: Microsoft’s $75 billion acquisition of video game maker Activision and Amazon’s deal to buy Roomba maker iRobot with investigations. Ofcom said it was concerned that, left unchecked, the concentration of cloud computing supplies in the hands of a small number of large US companies could lead to UK customers paying more and smaller groups being forced out of the market.