The LSE has fought tooth and nail to keep away from the grip of the Nasdaq.
The competition authority said the two must ensure the independence of the LSE's clearing services, LCH.
The LSE is also said to be in talks with Euronext, Europe's Nasdaq-equivalent electronic exchange.
The LSE's chief executive, Carla Furse, had rejected the offer as undervaluing the exchange.
"What the LSE is saying we dispute, " he told BBC Radio 4's Broadcasting House programme.
The Canuck challenge to what it regards as the LSE's imperial ambitions may not succeed.
The LSE says crossly that the table does not capture excellence in social sciences.
But a spokesman for the LSE told Reuters that trading would be as normal on Monday morning.
Both bidders were also warned not to obstruct access to the LSE's clearance provider by any competitor.
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The Grantham Institute at the LSE has released a briefing paper about the economics of wind power.
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"I'm also surprised that the LSE's consent wasn't sought, although this wasn't a formal LSE visit, " he said.
The LSE said that the BBC journalists had used a university society to set up the controversial trip.
Far more important, to them, would be the kind of long-term strategic choices highlighted in the LSE's report.
It was only in 2003, says Julian Le Grand of the LSE, that Mr Blair had his epiphany.
It's not hard to see two leagues forming--one linked with the NYSE, the other including the LSE and Nasdaq.
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There has even been speculation that Euronext and Deutsche Boerse could merge with each other, leaving the LSE isolated.
It was part of the LSE undergraduate program in that decade for example.
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"This was not an official LSE trip, " Craig Calhoun, the director of the LSE, said on his Twitter account.
It is the second time Deutsche Boerse has failed to buy the LSE.
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But Mr Seifert still talked defiantly of another, future bid for the LSE.
The LSE lacks a derivatives business, the fastest-growing area of trading these days.
Macquarie has tried to quell the fear that it would charge the LSE's users more than they pay now.
The offer for the LSE, which Macquarie will pursue as part of a consortium, would involve a similar structure.
But if Euronext decides to abandon the LSE too, it will be left with no suitors and little clear direction.
But Nasdaq already has servers humming in London, and Greifeld has exported Nasdaq's pay-to-play strategy to compete with the LSE.
The LSE will deliver a second report in May, weighing the costs and benefits to the taxpayer of an amnesty.
The LSE study concluded that immigration had probably increased productivity because skilled migrants had relieved bottlenecks in the labour market.
Sensing the mood, Macquarie Bank has reportedly asked to meet investment banks as it ponders a bid for the LSE.
The LSE's shares have risen steadily of late, though they fell back slightly on the morning that Macquarie went hostile.
The LSE counts 350 companies from over 50 countries on its markets, including American Express, BP, General Motors and Vodafone.
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