You're correct that it's called copyright infringement, but it's not strictly an offence - it's a tort. Copyright holders can in certain circumstances sue for damages, but you cannot be prosecuted by the crown. Making an illegitimate copy for profit or in order to harm the copyright holder, though, is a criminal offence (see section 107 of the Copyright, Designs and Patent Act 1988[1]).
[1]: https://www.legislation.gov.uk/ukpga/1988/48/section/107