Britain's House of Commons plans to vote Wednesday on a bill authorizing Prime Minister Theresa May to start exit talks with the European Union — the first major test of whether lawmakers will try to impede the Conservative government's Brexit plans.

The vote comes after two days of debate in which both government and opposition lawmakers said they would respect voters' June 23 decision to leave the EU and back the bill.

But the pro-independence Scottish National Party will try to pass a "wrecking amendment" blocking the start of divorce talks because the government has not disclosed detailed plans for its negotiations with the bloc.

The opposition Labour Party says it will try to amend the bill, but at a later stage. The bill is due to return to the House of Commons for a final vote next week before moving on to Parliament's upper chamber, the House of Lords.

The government wants to have the bill approved by early March so it can meet a self-imposed March 31 deadline for triggering EU divorce talks.

Meanwhile, Britain's former top diplomat to the EU warned Wednesday that disentangling the U.K. from the bloc will be a long and arduous process.

Ivan Rogers, who resigned in January after telling the government that a deal could take a decade, told Parliament's European Scrutiny Committee that Brexit will involve "a negotiation on a scale we haven't experienced, probably ever."

"This is going to be on a humongous scale," he said.

Rogers said consensus among the other EU nations was that a new free trade deal between Britain and the bloc would take until the early 2020s to be ratified.

One major wrangle is likely to be over how much Britain will have to pay the EU to leave. Rogers said EU officials currently put the figure at 40 billion to 60 billion euros ($37 billion to $56 billion).