A little-known Dutch advocate-general is poised to play king-maker in the €71 billion (£48 billion) bid battle for ABN Amro when he delivers his legal advice over the controversial side sale of the Dutch bank’s American unit.

Levinus Timmerman, a professor at the University of Rotterdam, has been nominated to advise the Dutch Supreme Court on whether it should require that the sale of LaSalle be put to a shareholder vote. Sources watching the bid battle have suggested that Professor Timmerman could deliver his recommendation to the highest civil court in the Netherlands as early as today.

His verdict is likely to sway the Supreme Court, whose only other evidence is submissions by lawyers representing the parties involved.

The court is due to rule in mid-July whether to force ABN, which sold LaSalle to Bank of America in April for $21 billion (£10.5 billion), to put the deal to a vote at an emergency shareholder meeting.

A spokeswoman for the Supreme Court said last week that Professor Timmerman, a professor in enterprise law, would be delivering his recommendation, but would not be drawn on when. The court will make his submission publicly available.

Last week analysts predicted that the chances of the Supreme Court waving through the sale without a vote were about 30 per cent. Either way, the ruling will be central to the unfolding struggle for control of ABN Amro between Royal Bank of Scotland and Barclays. The winner will complete the biggest takeover in banking history.

Jean-Pierre Lambert, banks analyst for Keefe, Bruyette & Woods, said: “There are so many probability trees in the ABN situation. We have to deal with one event at a time. The first is the recommendation by the advocate-general; then there is the decision of the Supreme Court.

“If the court reinforces the earlier judgment by the Enterprise Chamber, then we will see whether the RBS consortium can settle with Bank of America. But we also have to see what Barclays will do; its bid is conditional on the LaSalle sale. It is not yet clear what the central bank’s position will be. All of these key events are due to take place around mid-July.”

Deal observers believe that, should a LaSalle vote be called, a brief window of opportunity would open up for RBS and its consortium partners at Fortis and Santander, to thrash out a legal settlement with Bank of America.

The Wall Street giant had threatened to sue any party that disrupted its LaSalle acquisition, but is thought to be prepared to strike a compromise deal involving breaking up parts of the American unit and selling them, possibly to RBS.

Mr Lambert said: “All in all, the RBS consortium looks more likely to win in our view, because its offer is in large part cash and its higher cost synergies allow a higher offer price.”

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