For the past two years, Legal Week's UK Top 50 rankings have not been hugely impacted by merger activity, but 2017-18 got off to a bang with the three-way union of CMS, Nabarro and Olswang and Norton Rose's long-awaited takeover of Chadbourne & Parke.

These deals, along with this February's transatlantic tie-up of Eversheds and Sutherland Asbill & Brennan, will significantly reshape the upper echelons of the UK legal rankings, and many in the market say the change will not stop there, amid much anticipation of a long-predicted wave of law firm consolidation.

The three-way CMS merger and the Eversheds Sutherland tie-up will each add more than £200m to the top line of each firm, and these deals look set to redefine the UK revenue rankings in a way that has not been seen since the first half of this decade, when Lovells, Norton Rose, Ashurst and Herbert Smith all carried out major mergers.

In contrast, the only major mergers to impact this year's results were Wragge Lawrence Graham & Co's tie-up with Canada's Gowlings, which pushed the combined firm up eight places to 15th, and Irwin Mitchell's first full year of revenues derived from its 2015 takeover of Thomas Eggar.

Not that the market has been short of merger speculation – far from it. Rumours have included US firm Shearman & Sterling being linked with both Allen & Overy and Ashurst, and Berwin Leighton Paisner (BLP) with Norton Rose Fulbright, but with the firms in question denying any talks, many of the discussions being touted in the market have little – if any – substance to them.

I have a feeling we will see three or four big mergers over the next 12 months, particularly in the upper end

Dominique Graham, a partner in the professional services group at recruitment consultant Signium (formerly known as Graham Gill), suggests that many law firms have become nervous as a result of the consolidation that has happened around them over the last few years.

"Some firms react to triggers and take a more defensive stance," she says. "That is one of the main reasons why we are getting a lot of talk with nothing happening. Not many within firms are strategically positioned. There's a lack of strategic insight and vision, and a fear of change."

Furthermore, a number of proposed deals have been called off during the past two years, which has also heightened nerves.

Failed talks include BLP's attempted merger with Greenbergy Traurig in March last year, while Addleshaws' discussions with US firm Hunton & Williams and Germany's Luther also amounted to nothing. Other aborted deals in 2017 include Weightmans and Ward Hadaway and Ince & Co and Hill Dickinson.

Simmons managing partner Jeremy Hoyland explains why his firm – which has been seeking a US merger for years and in 2010 held early stage talks with Mayer Brown – is taking a cautious stance.

"Our view on merging is that there are of course some very good US firms that could be potential merger partners, but there are also a whole heap of challenges which make it a less attractive proposition for us," Hoyland (pictured) says. "We speak to law firms all the time. Of course I think if it was a good US firm, with a similar profile, fit and culture, then absolutely we would engage. But we're not currently involved in merger discussions."

Trowers & Hamlins managing partner Jennie Gubbins argues that her firm is reluctant to risk losing its brand and identity. "You'd need to feel there's an amazingly good reason to give that up. We are resolutely independent and want to remain resolutely independent."

Even Clyde & Co chief executive Peter Hasson, who has led the firm through a string of mergers and team acquisitions including the 2011 union with Barlow Lyde & Gilbert and its 2015 tie-up with Scotland's Simpson & Marwick, does not mince his words when it comes to mergers. "Merging would be one of the last methods I would use to develop the business, because there is a lot of dislocation," he stresses.

Meanwhile, RPC managing partner James Miller believes Brexit has had a limiting effect on merger possibilities. "When I first became managing partner in February, I got quite a few calls from potential partners in the US. There may be lots of talk about it, but I'm unaware of anything concrete. I think given you have got to be more cautious on the strategy side until we have a better view of what things look like due to Brexit."

In contrast, law firm consultant Alan Hodgart believes that 2017-18 is likely to see a spike in merger activity.

"I have a gut feeling we will see three or four big mergers over the next 12 months, particularly in the upper end. I can see three or four; two transatlantic and two local.

"I think a lot of it is due to the issue of scale. Firms are questioning whether they are too small at 500 lawyers, given CMS has more than 1,200. Some of the bigger firms have just got a lot bigger. There's also this realisation on profitability about overheads; the cost of investments in technology, for example, which are cheaper per head for a larger firm."

DAC Beachcroft managing partner David Pollitt agrees: "I think some firms will be looking to merge with other firms to create more scale and capability and international dimension."

Early indications are that the pair are likely to be right. In addition to the CMS union, which went live on 1 May, and Eversheds' combination with Sutherland, which went live in February, Scotland's Maclay Murray & Spens is merging with Dentons, DLA Piper has snapped up smaller firms in Denmark and Portugal, and Bond Dickinson will merge with US alliance partner Womble Carlyle Sandridge & Rice to form Womble Bond Dickinson.

With firms having to deal with pressure from new entrants, increasing globalisation and advancing technology, Eversheds Sutherland co-chief executive Lee Ranson says he has "little doubt" that consolidation will continue.

"Part of that is driven by the economies that come from mergers, part of it comes from the fast-forwarding of strategies to grow businesses in other markets, and part of it comes from creating organisations with the economic wherewithal to make investments in things like technology that will set them apart."