These rules apply to the EC “single market” and therefore may change post Brexit.
Currently the distance selling threshold for selling into UK is £70,000 or €100,000
If your dispatches from Ireland exceed €635,000 per annum or total arrivals from other Member States exceed €500,000 per annum you will be required to complete Irish Intrastat Returns.
A Vat Information Exchange System (VIES) Return would also be required to be completed in respect of the EC supply of goods.
Boxes E1 and E2 on your VAT return are used to record EC Transactions of goods.
If a non-established business sells goods within the UK the VAT Registration threshold is £1.