The treaty does not say how this process of notification should happen.
It has always been assumed that this would come in the form of a letter from the prime minister to Donald Tusk, the European Council president, and the timing would be in the hands of the British government.
But Professor Wyatt, who has represented clients in hundreds of cases before the European courts, said that EU lawyers might consider any discussion about Brexit between Mr Cameron and Mr Tusk and other EU leaders as effectively notifying the European Council of the UK's intention to leave.
Professor Wyatt said: "If David Cameron attends the European council on Tuesday, he is likely to confirm in discussions with other heads of government that the UK intends to leave the EU.
"He might do this directly in so many words or he might conduct conversations predicated on the UK's departure from the EU, such as suggestions that informal pre-negotiations might take place before Article 50 is formally triggered.
"EU lawyers might advise the council that such confirmation or such conversations are themselves enough to trigger Article 50 and set the clock ticking on the two year period for negotiating a withdrawal agreement."