Dec 16 (Reuters) - Britain"s competition watchdog said on Thursday a UK telecom tower deal between Spain"s Cellnex (CLNX.MC) and Hong Kong-based CK Hutchison (0001.HK) may raise "significant competition concerns" and risked higher mobile charges. The Competition and Markets Authority (CMA) said its investigation found that CK Hutchison should have sold its passive infrastructure assets, including towers and masts, to an alternative buyer rather than market leader Cellnex. Cellnex last year agreed to buy 24,600 telecom towers across Europe from CK Hutchison, which owns the Three mobile network in the UK, for 10 billion euros ($11.31 billion). "CK Hutchison had a range of options to commercialise these assets and the deal with Cellnex was not the only option available to it to pursue its broader commercial objectives," the CMA said in a statement on Thursday. The regulator said the sale could result in higher prices or lower quality services for mobile network operators, with a knock-on adverse impact for users of mobile networks across the UK. Cellnex said it was reviewing the CMA findings and would respond with any "practical alternative remedies" the company wishes the regulator to consider. It added that it continued to believe the deal would improve mobile coverage, including 5G, across the UK. CK Hutchison said it strongly disagreed with CMA"s findings and would be responding to the issues raised by the regulator. The CMA launched an inquiry into the proposed deal in May and referred it for an in-depth investigation in July. ($1 = 0.8844 euros)