If you trade goods within the European Union (EU) and their value exceeds the threshold or thresholds set for that year, you must complete and submit Supplementary Declarations (SDs) for Intrastat. Any VAT-registered business that has 'Arrivals' (goods acquired from suppliers in other EU member states) or 'Dispatches' (goods supplied to customers in other EU member states) with a value above the threshold has to complete and submit SDs. The current thresholds are £1.5 million for Arrivals and £250,000 for Dispatches.
Intrastat and SDs do not apply to the supply of services.
This guide explains the process of submitting your Intrastat Supplementary Declaration.