About €100bn of Irish securities moved from London to Brussels over the weekend as UK and EU markets deepen their split following Britain’s departure from the single market.

Holdings for 50 companies listed on the Irish stock exchange moved from the securities depository of the London operation of Euroclear, one of the world’s largest settlement houses, to its Belgium-based unit.

The two-year project to shift billions of euros of assets between depositories, which hold assets on behalf of investors and finalise transfers between customer accounts, is unusual.

Companies and investors do not often move corporate securities from settlement houses, an unglamorous but vital part of the market where deals are finalised and assets transferred from seller to buyer.

However, Brexit has changed the web of cross-border financial markets links in Europe. Ireland, uniquely among EU countries, does not have its own securities depository and its stock exchange has historically used the UK registration system, called Crest.

Around 90 per cent of all securities quoted on the Irish exchange also have a listing in London, and it has been easier for investors to settle deals using deposits held on account at the Bank of England. Only a third of transactions in Irish securities are settled in euros, with the majority settled in pounds and US dollars.

EU regulators have sought to reduce their reliance on London for financial services since the UK said it would diverge from EU standards.

Eurozone authorities also want more direct control of euro-denominated assets in response to concerns that countries outside the bloc could hit their critical market infrastructure with sanctions. More than €8bn a day of EU share trading has already moved from London to the EU, as has around 20 per cent of the euro derivatives trading market.

“You can say it’s unique. I don’t know of any other precedents to this. It’s been a mammoth task for all parties involved,” said Hardeep Tamana, managing director of Avenir, Ireland’s largest debt registrar, of the weekend’s transfer of assets.

Although owned by the same parent, Euroclear, the British and Belgian businesses are legally distinct. Companies and banks have had to amend contract and settlement instructions.

The switch has required shareholder approval from companies and many finalised their papers weeks before a February deadline set by Euronext, which owns the Irish stock exchange. Some London-based investment banks have also been scrambling to update their back-office operations and prevent a rush of failed trades in the coming days.

Brussels granted temporary permission for EU investors to continue to use the main UK securities depository after the UK’s departure from the single market, to give the market more time to prepare to move the assets to the eurozone. The permit, known as equivalence, is one of only two the EU granted the UK and will expire at the end of June.