Large law firm mergers have delivered above-average increases in profits, especially those based on expanding the scope of practices, rather than their scale, figures released at the conference revealed.

Research by law firm consultancy Altman Weil, based on 17 mergers involving 300-plus lawyers, disproved conventional wisdom that profits per partner (PPP) do not grow in the short term after merger because of the associated costs, with the firms seeing an average 18% rise over the first two years.

In the long term, those firms that merged before 1999 have seen a 21% increase in PPP, compared to 13% for the top 100 US firms collectively over that period.

The survey mainly focused on US mergers in the past decade, but included Clifford Chance's tie-up with New York's Rogers & Wells, and the 1996 merger of Dibb Lupton Broomhead and Alsop Wilkinson to produce what is now City firm DLA.

The survey found that in the first two years, those mergers that aimed to add scale saw an 8% rise in PPP, while those geared at widening the practices' scope saw a 22% jump, with those that combined the two at 21%.

'In a sense, that is understandable, as scale mergers require greater integration of cultures earlier, and thereby could be expected to be more disruptive,' the survey said.

DLA chief executive Nigel Knowles told the session on mergers that it is 'best to crash the firms together as soon as possible' after merger, rather than have a long drawn-out integration process 'which can depress people'.

He also stressed that it is vital for merging firms to set their strategic vision at the start, saying he 'wasted two years' after the 1996 merger because they did not do that.

Stephen Denyer, City firm Allen & Overy's regional managing partner for Europe, advised merging firms not to provide 'an unduly rosy picture' of themselves, to work together for a substantial time before making a final decision, and to ensure, as far as possible, that the financial terms are neutral.

'Neither firm should pay for the goodwill of the other,' he said.