A year after it was proposed, the £31.4bn ($44bn) merger between Telefónica’s O2 UK subsidiary, and Liberty Global’s Virgin Media – the UK’s largest cableco – has been approved by regulators. It is one of the UK’s largest ever telecoms deals, far higher than the £12.5bn price BT paid to acquire MNO EE in 2015. That is partly down to the strong job O2 UK has done in the past year to strengthen a business that often struggled in the 2010s, but has now leapt from third to first place in terms of subscribers. The two parent firms have promised to invest £10bn in the UK over the next five years and create “a stronger fixed and mobile competitor in the…