Consumer confidence is at its lowest level for six years because of Brexit.
A new report from the Banking and Payments Federation also shows that the tourism and construction sectors are worst affected.
The BPFI says employment and tax revenues are also vulnerable in the event of a no-deal Brexit.
Annette Hughes, one of the authors of the report, says consumer confidence is key for all small and medium enterprises.
"It's really important that consumers feel confident about the overall state of the economy, about their personal financial situation and their ability to make purchases," said Ms Hughes.
"And equaly we need to see confidence among businesses. That's all very good for SMEs."