The Obscene Publications Act 1959 applies to all published material whether on the internet or offline. Material is published if it is circulated, distributed, sold, given, lent or offered to another person. It will be deemed to be obscene if the court finds that its effect is such as to tend to deprave and corrupt persons who are likely to read, see or hear it.
The Criminal Law Subgroup of the Home Secretary’s Task Force on Child Protection on the Internet has considered the implications of a judgment in the Court of Appeal (R v. Perrin  EWCA crim 747) which indicated that where children are likely to access material of a degree of sexual explicitness equivalent to what is available to those aged 18 and above in a licensed sex shop, that material may be considered to be obscene and subject to prosecution. This applies to material which is not behind a suitable payment barrier or other accepted means of age verification, for example, material on the front page of pornography websites and non-commercial, user-generated material which is likely to be accessed by children and meets the threshold.