"We are specifically advising businesses to take some simple steps to be prepared."
HMRC is urging business owners to consider three steps to ensure they can continue to trade with the EU if the UK leaves without a deal.
Firstly, businesses are urged to register for an Economic Operator and Registration Identification (EORI) number, which is currently not required for firms who only trade inside the EU.
In the event of a no-deal exit, businesses will be unable to continue trading with the EU without an EORI number; however, HMRC figures show that so far just 17% of these businesses have registered.
After getting an EORI number, HMRC says businesses need to consider how they want to make customs declarations.
For businesses that import goods into the UK from the EU using roll on, roll off locations, they can take a third step and register for new Transitional Simplified Procedures (TSP). TSP will allow businesses to import without having to make a full customs declaration at the border, and postpone paying any import duties. For imports using other locations, and for exports, standard customs declarations will apply.
HMRC has written directly to 145,000 VAT-registered businesses that only trade with the EU advising them to start their preparations and apply for an EORI number.
There are another estimated additional 95,000 non-VAT registered businesses that also need to take action, however HMRC says that only 40,973 businesses have registered for an EORI number.
To help businesses make import and export declarations, HMRC has made £8 million in funding available for traders and intermediaries to support them with training and IT costs.
Financial secretary to the Treasury, Mel Stride, said: "We want businesses to be able continue trading with minimal disruption in any scenario but we also know that people tend to leave things until the last minute and we would urge against that.
"We are specifically advising businesses to take some simple steps to be prepared – the first thing they need to do is register for an EORI number - it is free and takes less than 10 minutes.
"Step-by-step advice can be accessed via GOV.UK – the help is there, we just need business owners to take action."