Hard on the heels of Halliwells' takeover of Manchester insurance stalwart James Chapman & Co comes another important northwest merger – this time from the other side of the tracks.

Irwin Mitchell has snapped up the claimant boutique Alexander Harris. In the field of personal injury, this is a top-level transaction. Despite the loss of some key partners in recent years, Alexander Harris remains a highlyrated clinical negligence outfit.

The similarity between the Halliwells and Irwin Mitchell deals goes beyond geography. Just as James Chapman was struggling to survive on its own in the cut-throat world of defendant insurance, eight-partner Alexander Harris, too, was evidently facing the squeeze. Irwin Mitchell's stellar profitability – at least when measured by average profits per equity partner – is testament to the fact that, if managed efficiently, claimant work can be highly profitable. Scale is a crucial part of this equation – not just for low-value bulk work, but also for high-value cases.

Clinical negligence cases can drag on and are difficult to prove. The rewards can be high if you win, but smaller firms risk becoming dependent on a handful of cases, exposing them to cash-flow and risk management problems. All of which, say senior personal injury lawyers, makes the logic of the Alexander Harris/Irwin Mitchell deal compelling.

The Legal Week top 50 survey contains just two firms with large claimant practices: Irwin Mitchell and Shoosmiths. Both have performed well in recent years. Irwin Mitchell's average profits per equity partner for 2004-05 of £490,000 put most national firms in the shade and not a few leading London practices. Shoosmiths – a Legal Week 'firm to watch' in last year's analysis – was the fastestgrowing top 50 firm by profits in 2004 and 2005.

The pair's unpretentious approach to legal business is epitomised by Shoosmiths' view when reviewing its bulk practices. Far from being embarrassed about this work, partners argued that the commercial nous required to produce the legal equivalent of widgets actually brought it closer to many of its business clients. With the Clementiinspired legal services reforms and the Carter review of criminal legal aid promising to transform so-called high street practice, expect the Legal Week top 50 to become more, not less, diverse.