A new national legal giant is on the verge of being created that would be equipped to take on Scotland's ''big four'' law firms on their own patch.

Pinsents, which has offices in Birmingham, Leeds, London and Manchester, is set to merge with Masons, which is principally based in London but also has offices in Glasgow and Edinburgh which together employ over 50 fee earners.

The deal - the biggest UK law firm merger in four years - would create a ''top 15'' firm with annual revenues of more than (pounds) 150m, 240 partners and nearly 900 lawyers in total.

A partners' vote will take place by the end of the month. If the proposal receives the go-ahead, it will herald a major expansion of the newly-enlarged firm north of the border.

Few of the big established UK law firms have entered the Scottish market to any great extent, with the singular exception of top 10 outfit DLA.

Indigenous market-leaders Dundas & Wilson, McGrigors, Maclay Murray & Spens and Shepherd+Wedderburn continue to prosper in their absence.

Masons, a 100-partner international firm that opened in Scotland five years ago, ploughs a highly lucrative furrow in the sectors of information technology, construction and engineering, infrastructure and energy.

The larger Pinsents, by contrast, is driven by its corporate practice. Merging the two will create a major player with the breadth of expertise to compete with Scotland's other major corporate law firms across a whole range of disciplines.

One legal industry expert commented: ''If the merger gets the go-ahead it is realistic to expect major growth at the Scottish offices, particularly in the areas in which Pinsents specialises.

''They are particularly strong in financial services and banking.''

Pinsents and Masons currently have average partner profits of about (pounds) 270,000 and (pounds) 247,000 respectively. Neither firm would comment on the merger plan.