After the shareholder approvals, all that is required now for the €24bn merger of the London Stock Exchange Group and Deutsche Börse to become a reality are the regulatory approvals.

That summing-up, of course, belies the difficulties. This has always been the area where the toughest obstacles lie.

Of the many antitrust and prudential authorities around the world looking at this deal, the three biggest lie in the exchanges’ home countries and the EU in Brussels. And an already-tough decision has been hugely complicated by the UK’s Brexit vote.

The concerns of German politicians and some regulators have been well aired— theirs is largely about a loss of oversight of their exchange infrastructure to a country that will not be in the EU. Even so, they have been noticeably quiet of late.

Last month the European Commission formally opened its own antitrust investigation. Market participants have filled out the questionnaires they have been sent, one of which has been seen by the Financial Times. Many of the questions focus on indices and the possibility of the deal forcing up the price of market data. Whether the commission will receive full answers is also another matter. Many banks are potentially compromised because they are also on the M&A ticket.

In reading the questionnaire, there is also a sense — right now — that Brussels may not be the hurdle people think it will be. There is not the same killer argument against the deal as there was with the NYSE Euronext-Deutsche Börse merger four years ago. Dutch, Portuguese and Belgian letters to Brussels outlining their concerns have mainly focused — with remarkably similar wording — on the impact on their small and medium sized businesses. But this deal is not about that, it is about derivatives, data and risk management.

The commission says it will treat the UK as part of the EU but that is not the impression one gets from the questionnaire. For example, in the section on cash equities, it asks about competition in trading and clearing of German-listed equities but not in the UK.

In the derivatives section, it asks questions about Eurex’s over-the-counter clearing business but few of LCH. Question 184 and 186 ask about shifting the open interest of derivatives from LCH to Eurex OTC Clear, but not the other way round. An alternative reading for this impression is that it is because Deutsche Börse operates a vertical silo for trading and clearing of equities and derivatives — in contrast to LCH. No doubt the expected Phase 2 in-depth investigation is more rigorous.

Post-Brexit vote, the biggest unknown now lies with the attitude of the new, more conservative UK government and how it feels about the deal.

Theresa May, prime minister, says she will not show her Brexit hand, assuming she has one. Quickly killing the deal would be one of the clearest signals that the City has of the government’s vision of the future.

Yet we have been promised that the deal terms will be unchanged. However, already Deutsche Börse altered the terms by which the deal would gain acceptance from shareholders. There are noises coming from Germany that there could be a dual holding company, instead of a single London-based holding company as planned.

Germany has also made a pitch about shifting euro-denominated clearing business to Frankfurt; anecdotal perhaps but enough grey to give a nationalist politician unease.

More than that: the UK may ask whether now is the time to judge an overseas combination involving major domestic market infrastructure, when no one knows what its relationship with Europe will be. “Come back in two years,” they may argue.

Does the UK has the legal capacity to intervene? History and indeed this industry are littered with examples illustrating that where there is a political will, there is a legal way.

This article has been amended to make clear that the issue being raised about a combined London Stock Exchange Group and Deutsche Borse concerns the location of its holding company, rather than its headquarters.

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