Britain's CREST financial markets settlement system went down on Friday after suffering technical issues but should be up and running before the market reopens next week, owner Euroclear said on Saturday.
The Bank of England, which uses the CREST system, switched to back-up procedures to ensure settlement of transactions.
CREST is the central securities depository for share and UK government bond markets in the United Kingdom and for Irish stocks, settling trades as the final leg of a transaction.
Euroclear said it had no reason to believe the outage was caused by a cyber attack.
"We can confirm that Euroclear UK & Ireland has experienced an internal technical issue resulting in a settlement outage," a Euroclear spokesman said.
"We have invoked our contingency solution, Non Standard CREST Closure, in coordination with the Bank of England. This process, which is regularly tested, ensures that the impact to financial market participants is minimised."
He said they expected services to be resumed on Monday.
"Investigations are being carried out and we are taking all necessary actions to remedy the situation," he added.
There were no immediate details on the volume and value of transactions affected.
"We are aware of an issue with CREST settlement. We are liaising with EUI - who are responsible for CREST – and are working to help them resolve the issue as quickly as possible," the Bank of England said in a statement.