Cast your mind back five years ago to what seems like a different era. Clyde & Co was generating not much more than half its current revenues and Holman Fenwick Willan barely scraped into the top 40 while Ince & Co just about made the top 50. Kennedys was nowhere to be seen. Corporate markets were booming, and transaction-driven law firms were really just getting into the swing of the credit boom.

Little wonder that insurance-driven law firms were overlooked as the script for global law was written – the sector was associated with nothing more glamourous than brutally executed panel reviews and misconceived cross-selling (Barlow Lyde & Gilbert's lost years and Davies Arnold Cooper's 'pillars of strength' spring to mind).

Apart from the startling growth Clydes was already demonstrating, powered by global expansion and a strategy that largely went over the heads of journalists such as, well, me, there was little sign of the breed's future ascendency. Step forward, and it's a very different story, with insurance and transport law firms now having led the pack consistently since the credit crunch hit four years ago.

And surely the clearest signal of insurance law asserting itself on the wider stage is Clydes' upcoming merger with Barlows, which we assess in detail this week. On paper, at least, the deal looks impressive. On one hand, you have in Clydes one of the most successful and best-run firms in the top 50. As the smaller partner, Barlows clearly has had its issues. It had showed signs that it could stabilise itself and even go forward independently, but in truth once its aviation team quit in March, its options rapidly narrowed.

As such, throwing in with Clydes seems an admirably pragmatic response. But even diminished, it retains some excellent teams, and lopsided mergers typically work better in law firm land than the equal partner deals, which are usually beset with post-union jostling. The creation of an EC3 giant also looks set to position Clydes for a fast-consolidating insurance industry; it's an irony that insurance law firms have thrived at a point in which their clients have come under pressure.

And insurance and related trade and transport disciplines offer huge opportunities internationally, partly because other legal markets have not created similar specialist law firms. That dynamic is stark in the US, where Clydes has made the kind of no-fuss progress the magic circle can only dream of. Still, good as it looks in theory, there will be some cultural kinks to work out.

Clydes spent years rather successfully destabilising its old rival, including hiring some influential partners that will now be rubbing shoulders once again with their former colleagues. And the question remains what will happen to Clydes when its highly-regarded and long-serving senior partner Michael Payton finally stands down. Because strong as the combined Clyde & Co looks, there will be no shortage of able challengers planning to steal its lunch.