Slaughter and May, Allen & Overy (A&O) and a trio of Indian law firms have taken lead roles on the multibillion-dollar merger of Vodafone India and Indian telecoms company Idea, a deal that will create the country's largest telecoms operator.

The merger, which is slated to close in 2018, will create a combined company valued at more than $20bn (£16bn), boasting 400 million customers, 35% customer market share and 41% revenue market share.

Slaughters and Indian firm S&R Associates are advising Vodafone India, while A&O and Indian firms Vaish Associates Advocates and Bharucha & Partners are acting for Idea.

A&O is acting as international counsel for Idea with a team led by London finance partner Sanjeev Dhuna and London corporate partner Tom Levine.

Slaughters has been Vodafone's go-to M&A firm in recent years, taking the trophy role on the 2013 sale of its $130bn stake in Verizon Wireless to US telecoms group Verizon Communications, one of the largest deals in history. The firm also advised last year's joint venture with US cable giant Liberty Global, which saw the companies merge their Dutch operations to create a Netherlands-wide communications provider.

Slaughters M&A head Roland Turnill took the lead on both of those deals, with corporate partner Susannah Macknay also advising on the Dutch deal and corporate partner Nigel Boardman and finance partner Craig Cleaver acting on the Verizon sale.

Linklaters has also taken a number of M&A roles for Vodafone in recent years, including its 2013 acquisition of German cable TV firm Kabel Deutschland.

The deal takes place in the context of significant competition in the Indian telecoms market following the launch of mobile operator Jio by India's richest man, Mukesh Ambani, in 2016. According to The Economist, Ambani has since invested $25bn (£20m) in Jio, and amassed 100 million customers in the past six months.