The value of mergers and acquisitions in the first half sank by nearly a third from the same period last year to $1,860bn (£935bn) as the collapse of the buy-out boom prompted a steep drop in the number of highvalue deals.

The raw number of deals announced in the first half of the year topped the first half of 2007's total, according to preliminary figures from Dealogic. But while the five biggest deals announced in the first six months of this year accounted for 15 per cent of global M&A volume, the overall number of transactions valued above $1bn dropped sharply.