They sought to reassure foreign financial firms that a no deal Brexit would not result in disarray for the City of London at a time when many banks, insurers and asset managers were already moving staff and operations to new EU hubs.
Lawmakers vote on Tuesday in a bid to end a deadlock over Britain's divorce settlement with the EU and prevent it leaving with no deal on March 29.
EU financial rules are being embedded into British law, but changes are needed to make them work properly as Britain falls outside the purview of EU regulators.
Lawmakers are scrutinizing measures known as statutory instruments (SIs) to give ministers and financial regulators powers to largely bypass parliament to push through changes.
Nicky Morgan, chair of parliament's Treasury Select Committee, told Britain's financial services minister John Glen that while the powers showed that finance would be prepared for all eventualities, full parliament should debate them.
"We can understand why the powers are needed but they are unprecedented. Having the SIs in place is an important message to the world," Morgan said.
Glen said Britain would be in uncharted territory if there is no deal.
"The predominant message I have is that we need to secure a deal. Equally it would be imprudent and irresponsible not to have a fully functional regime in a no deal situation," Glen said.
"In the event of a no deal Brexit, we won't have vast parts of the financial services sector saying 'well, we didn't know what was happening'," Glen added.
Andrew Bailey, chief executive of the Financial Conduct Authority, and Sam Woods, Deputy Governor of the Bank of England, said tweaks from the "massive operation" run to over 2,000 pages.
Bailey said the powers would only be used to keep regulatory system "where it is today", rather than make fundamental changes, and the vast majority of changes would be published.
(Reporting by Huw Jones; Editing by Alexander Smith)
By Huw Jones
