A bewildering flurry of deals between world stock exchanges has left two Gulf kingdoms with a near-50 percent stake in the London Stock Exchange between them.

Qatar had made a firm offer at £14 a share for most of the 31 percent stake in the LSE held by Nasdaq, the New York exchange, and was expected to succeed. But as part of a complex deal between Nasdaq and the Borse Dubai, 28 percent of the LSE was instead sold to Dubai.

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The Qataris responded swiftly, agreeing to take almost 21 percent of the LSE from two US funds, including the corporate raider Samuel Heyman, in an apparent spoiler to any hostile takeover bid for London from Dubai.

The LSE welcomed the arrival of the Qataris “as a long-term investor”. Significantly, no such announcement was made about Dubai.

The Dubai/Nasdaq deal stemmed from rival bids by both for another operator of world exchanges, OMX in Stockholm. The two have made common cause and agreed that while the Dubai offer, the higher of the two, will go ahead, any shares acquired, including the 28 percent already held as a result of a market raid next month, will go to Nasdaq.

For London, what had seemed a secure future with a supportive 30 percent shareholder in the Qataris is now much more uncertain.

Dubai is expected to at least consider a full bid for the LSE, whose shares leapt £2.34p to £16.87. This is significantly above the £15.85 the Qataris paid for their stake and suggests the market is expecting a takeover battle.

Last night, in yet another apparent spoiling move, the Qataris sent Citigroup on a raid into the market in Stockholm to sweep up a near 10 percent stake in OMX.