While the question specifically asks about UK law, similar principles apply in united-states law. Thus I will answer for the same issue in US law.
The relevant section of US Federal law is 18 U.S. Code § 2320 - Trafficking in counterfeit goods or services. This declares that anyone is a criminal who:
- (1) traffics in goods or services and knowingly uses a counterfeit mark ...
- (2) traffics in labels, patches, stickers, ... , or packaging of any type or nature, knowing that a counterfeit mark has been applied thereto, ...
- (3) traffics in goods or services knowing that such good or service is a counterfeit military good or service the use, malfunction, or failure of which is likely to cause serious bodily injury or death, the disclosure of classified information, impairment of combat operations, or other significant harm
- (4) traffics in a drug and knowingly uses a counterfeit mark ...
All of these refer to a person who "traffics" In this connection this will mean sells or tries to sell, or transports for sale, not buys.
Findlaw's page on "Buying Counterfeit Goods: Laws and Resources" says:
In the U.S., federal law protecting trademarks makes it illegal to knowingly traffic counterfeit goods, which includes the production, sale and transport of such goods. The U.S. Department of Justice, however, has stated that federal law doesn’t prohibit an individual from buying a counterfeit product for personal use, even if they do so knowingly.