Shares in the London Stock Exchange (LSE) have risen by close to 15% in London after the high-tech US Nasdaq Stock Market snapped up a stake.
Dealers are waiting to see if the Nasdaq makes a full bid
On Tuesday evening, the Nasdaq bought a 15% stake in the UK market at a price of £11.75 per share, in a deal worth £447.7m ($780m).
It came a month after the US group dropped a takeover of the LSE, when a £9.50-a-share proposal was rejected.
By the close, LSE shares were up 15.4%, or 160 pence, at £11.98.
Dealers are now watching to see if the Nasdaq makes a full bid at the £11.75 per share price.
The US group bought approximately 35 million shares in the LSE from Threadneedle Asset Management - the London market's biggest institutional investor.
Threadneedle confirmed the purchase, saying it had sold "substantially its entire holding" of the LSE, leaving it with a share of less than 1% in the company.
"We continue to believe that the LSE is the world's most successful cash equity trading platform, operating in the world's most successful financial centre, and are pleased to see this value recognised by the market," the firm said in a statement.
Nasdaq added it had also bought a further 2,695,735 shares to take its holding to 38.1 million shares, or 14.99% of LSE.
A spokesman for the Nasdaq said the move was a "very strategic purchase".