Shares of Facebook took another tumble today, continuing a downward spiral that began at the start of the week.

Facebook shares slumped to more than 10 per cent below their float price on their second day trading as a public company.

The chief executive of Nasdaq said the stock exchange is “humbly embarrassed” by its bungling of Facebook's hugely anticipated debut as a public company on Friday.

Facebook is officially the biggest internet flotation of all time, after the social network priced its shares last night at the top of its expected range and set a value for the company of $104bn (£66bn).

Facebook is bracing for increased scrutiny of its privacy policies and the way it makes money from data on its 900 million users, now that it is finally making its debut as a public company.

Mark Zuckerberg last night set out Facebook's plan for world domination, in a web video to promote the forthcoming share sale that could value the social network at up to $96bn (£60bn).

Shares in Zynga, the online games company behind the Facebook favourite Farmville, fell 5 per cent on their first day of trading on Friday.

Shares in the London Stock Exchange surged yesterday in the wake of the dramatic collapse on Wednesday of its merger with Canada's TMX on expectations that it would become a takeover target.

The Nigerian Stock Exchange (NSE) has discussed a possible tie-up with London, according to the head of the country's capital markets regulator.

Leading brokers warned that a takeover of the European clearing house LCH.Clearnet by an exchange will hurt competition.

Shares in DP World, the third largest ports operator in the world, are to start trading on the London Stock Exchange on 1 June, marking the effective return of P&O to the London market.