Top bankers were blindsided by chancellor Rishi Sunak’s snap decision to allow Britain’s smallest businesses to borrow up to £50,000 to see them through the coronavirus pandemic, according to reports.

The Financial Times says that over the weekend, leading City executives had based their plans on the assumption the limit would be £25,000, only for Sunak to unveil fully-guaranteed ‘bounce back loans’ of up to twice that threshold for micro-businesses on Monday afternoon.

Commercial banks are charged with administering the loans.

One banker tells the paper: “The industry has been left a bit shocked …There is now some urgent back-filling that needs to go on.”

Government sources tell the paper that the £50,000 figure was always floated as “an option” in conversations with banks, but confirm that lenders were not told about the limit until just before Sunak’s statement.

The scheme officially goes live next Monday, with the Treasury due to hammer out details including what happens in the event of default and the exact due diligence checks required for businesses to access the loans before then.

Commenting after the announcing of the scheme, Treasury select committee chair Mel Stride said: “I have called for government to consider 100 per cent guarantees for smaller-sized loans, so the introduction of bounce back loans is extremely welcome.

“However, the success of the new scheme will still depend on the actions of lenders. It is essential, therefore, that there is full and regular transparency on the progress of this scheme in order to get this further vital lending out the door fast.”