Parliament is sovereign and, if Brexit wins, Cameron will not be legally obliged to invoke the Lisbon treaty to start an EU exit

The simple answer to the question as to whether the EU referendum is legally binding is “no”. In theory, in the event of a vote to leave the EU, David Cameron, who opposes Brexit, could decide to ignore the will of the people and put the question to MPs banking on a majority deciding to remain.

This is because parliament is sovereign and referendums are generally not binding in the UK.

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An exception was the 2011 referendum on changing the electoral system to alternative vote, where the relevant legislation obligated the government to change the law to reflect a “yes” vote had that occurred. No such provision was contained within the EU referendum legislation.

In 1975, when the last vote on whether to stay in the EU (then the European economic community) was held, the rightwing Conservative MP Enoch Powell, unhappy about what he considered a loss of national sovereignty, argued that the result was merely provisional as it could not be legally binding on parliament.

If the British public votes on Thursday for Brexit it will be in the hands of Cameron to decide when to invoke article 50 of the Lisbon treaty, which represents formal notification of any decision to leave. The prime minister has said he would have to trigger it immediately after a vote, although this might have been a way of emphasising that there would be no going back, to people thinking of voting leave.

Some advocates of Brexit argue that discussions with other member states could start informally, without article 50 having to be invoked. There has even been the argument, made by some in the Brexit camp, that the mere threat of departure following a vote to leave could smooth the way to a better deal for Britain which could then be put to voters in a second referendum on EU membership.

The wrangling reflects the fact that there is no binding legal process to force Cameron to invoke article 50. In theory, he could ignore the public and disregard a Brexit vote. In practice he has repeatedly promised that the result will stick – and there may be no going back on that line now.