Stagecoach chief executive Brian Souter has added a further £6.4m to his vast personal wealth after exercising share options in the Perth transport giant.

Souter this week bought 4.36 million shares at between 27p and 85.75p apiece under options granted between 2002 and 2004.

The exercise netted Souter a paper gain of £6.4m, this being the difference between what he paid for the shares - £2m - and the value of that holding now, which is £8.4m.

Stagecoach shares closed at 192p on Wednesday.

Souter, who helped bankroll the Scottish National Party's Holyrood victory, has so far enjoyed an extraordinarily lucrative 2007. He recently pocketed more than £100m when the company returned £700m to shareholders, and was last week granted deferred bonuses worth nearly £800,000.

Souter retained the shares bought this week and now holds a 14.72% stake in Stagecoach worth £201m.

Souter's sister, fellow Stagecoach founder Ann Gloag, has an 11% stake in the company and pocketed more than £70m from the recent return of cash to investors.

In this year's Sunday Times richlist, Souter and Gloag rocketed from ninth to fourth in the league table of Scotland's wealthiest individuals, with an estimated combined fortune of £770m.

Last month Stagecoach posted underlying pre-tax profits of £162m, up from £117.1m in 2006.