These businesses, who are unfamiliar with international trade will have probably not have understood the full implications of the UK leaving the EU and will not be able to move goods in and out of the UK without one.
HMRC have written to these businesses to let them know the UK EORI number they’ve been assigned and the next steps they need to take.
For those businesses that are not VAT registered and do not have a UK EORI number, they must apply now at https://www.gov.uk/eori in order to commercially trade with the EU.
You can check the next steps you need to take to ensure that your business is ready for Brexit the UK Government Trader Checklist https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/826070/7239_EU_Exit_Simplified_Trader_Checklist_one_pager_v12_Access_KJ__2_.pdf
Additional information can be found including guidance can be found at https://www.gov.uk/topic/business-tax/import-export and also traders can sign up for updates at the EU exit update service at https://www.gov.uk/email-signup/?topic=/government/brexit