theresa may
British Prime Minister is expected to send a letter to EU leaders in Brussels this week, implementing Article 50 to kick off the process of divorcing the U.K. from the EU. Above, May at the EU summit in Brussels, March 9, 2017. Dylan Martinez/Reuters

As British Prime Minister Theresa May prepared to outline plans for divorcing the U.K. from the European Union, Labour Party spokesman Keir Starmer warned his party would block any deal that does not deliver same benefits the country currently enjoys.

May planned to trigger Article 50 to trigger the mechanism for leaving the trading block this week, more than nine months after Britons voted on the issue.

Read: How Much Could Brexit Cost The UK?

The Sunday Times reported May would send a letter to EU leaders in Brussels Wednesday, announcing the start of negotiations, a process that is expected to last two years, and the following day publish the government’s Great Repeal Bill, which converts EU law into British law. Opposition lawmakers are wary of the measure because it gives ministers wide-ranging powers to change the rules as they convert the statutes. The letter will detail key demands for an exit deal.

Meanwhile, the biggest investment banks already were beginning the process of moving some London-based operations elsewhere.

Opposition leader Jeremy Corbyn has said Labour members of Parliament will support an exit measure only if it guarantees “unfettered access” to the European market, something that already has been ruled out by the EU, which doesn’t want Britain to benefit from the exit.

Read: Populism, 'Brexit' And 'Frexit' Could Damage EU Economies

Corbyn told ITV Sunday if total access is denied, “the threat to jobs in this country is absolutely huge. Most of our manufacturing industries have a European sale and European supply chain in them. And if we don’t maintain this unfettered access to the European market then quite clearly those industries are very much at risk.”

Starmer, the shadow Brexit secretary, was scheduled to deliver a speech Monday in which the Guardian reported he will say the ideological approach to extricating the U.K. from the EU “would be disastrous and divisive.”

Starmer told the Guardian he will lay out six tests that must be met before Labour will support a deal, including guarantees of transitional arrangements, maintaining cross-border security and fair management of immigration.

“The truth is that Brexit cannot tackle stagnant wages, resolve a chronic skills gap, reduce unequal growth across the U.K. or improve underfunded public services,” Starmer is expected to say. “Brexit cannot mend public trust in politics or build more cohesive communities. And it cannot provide a place for Britain in a more complex and chaotic global order.”

Bloomberg reported Bank of America Corp., Standard Chartered Plc and Barclays Plc were considering moving operations to Dublin while Goldman Sachs Group Inc. and Citigroup Inc. have their eyes on Frankfurt, Germany, in case Brexit results in them not being able to sell services from London. Other cities likely to benefit include Paris, Amsterdam and Madrid.

London stands to lose 30,000 financial industry jobs and $1.9 trillion of assets after Brexit, the nondoctrinal Bruegel economic think tank has estimated.