Importing a car engine to UK from EU for Exchange unit

Hi I am considering Importing a car engine to the UK from the EU for repair or exchange and then exporting it back to the EU. The engine was UK-built originally. What are the duty implications? Thanks

Hi DiscoGruffalo,
Tariff rates can be checked by visiting trade tariff UK. 
Trade Tariff: look up commodity codes, duty and VAT rates
Importer may be able to claim inward processing relief if the goods are imported in to UK for repair.
Apply to delay or pay less duty on goods you import to process or repair
Thank you