Release to free circulation means removal of the goods from the customs warehousing procedure.
Paying duties on goods being released from the customs warehousing procedure
When your goods are released from the customs warehousing procedure, you may have duties and taxes to pay. You can work them out using:
the Tariff description (from Volume 2 of the Tariff) and rate of duty
the quantity and/or the value
HM Revenue & Customs' (HMRC) official rate of exchange
You may also have to pay import VAT at this time - read more about Classification rules and the Tariff. For further information you can find guidance in Notice 702/9 (VAT Imports CPEI procedures, end use and free zones) for import VAT.
The valuation of goods for the calculation of import duties is based - in a Type D warehouse - upon entry into the warehouse, while for A, C and E Type warehouses, the value of the goods is determined upon removal.