Senior bankers have played down the prospect of thousands of City jobs being lost in the aftermath of the vote for Brexit, because of the complexity involved in making the changes to adapt to the UK’s future relationship with the EU.

One likened the risks to financial stability to moving nuclear waste, amid warnings that financial firms needed time to make changes to their business to adapt to any new trade deal.

Douglas Flint, chairman of HSBC, said the bank was taking three years to move 1,000 roles within the UK to Birmingham. “Contemplating as a firm moving any number of people outside the country, setting up arrangements and getting licensed is a non-trivial task,” Flint told a House of Lords committee on financial services.

Before the vote, HSBC had said it could move 1,000 roles to Paris, and Flint had called for the UK to stay in a reformed European Union.

Sitting alongside him, Alex Wilmot-Sitwell, head of the European operations of Bank of America Merrill Lynch, warned that the two years to negotiate the UK’s exit from the EU after Article 50 is triggered was not long enough for firms to make changes to their business.

“The materials that are being moved are risky materials, and you don’t move nuclear waste in a race. You do it in a very carefully coordinated and managed process. The materials are perfectly safe, so long as they are properly handled and so long as the period of time to move them is suitable.”

It could take two to three years, said Wilmot-Sitwell. “It’s a multi-year process if it’s going to be completed safely and not going to risk financial stability,” he said.

Flint described London as an ecosystem which had provide a network of systems and regulation for efficient operations. “Dismantling that seems to be counterintuitive to anything that people have tried to do over the last eight years post-crisis.”

Were the City to lose the ability to clear trades in euros – as suggested by the French – Flint said “it would be very bad for the ecosystem” and “seriously damage” London.

But, he said, replicating all London’s financial services in another centre would not be achieved immediately. “I’m sure part of the discussion will be ‘you couldn’t replicate all of this in one place probably ever’,” said Flint. “There isn’t something that immediately replaces it.”

Wilmot-Sitwell said the financial services industry was not a Lego set that could be pulled apart without consequences for markets and customers.