The only images that it has been illegal to possess until now have been images of child sexual abuse. It has been an offence to publish obscene images, but not to possess them.
The new law, which is part of the Criminal Justice and Immigration Act of 2008, came into force on 26th January. The Scottish law is being drafted and will go further, criminalising the possession of images of rape.
Though the law has now come into force outside of Scotland it is unlikely to be aggressively enforced. The Association of Chief Police Officers (ACPO) has said that it will not pursue offenders, but will investigate any instances that it comes across of images that break the new law.
ACPO told The Guardian newspaper that the police "will not be actively targeting members of the public but will be conducting investigations into the unlawful possession of this material where found".
A statement from ACPO's lead officer on extreme pornographic images Jim Gamble said that the new law "will assist law enforcement officers when presented with future investigations where indecent and illegal material is found".
"Whilst the publication and distribution of extreme pornography is already covered in UK legislation through the Obscene Publications Act 1959, the new criminal offence of possession of this material has been created in order to prevent the further circulation of what is sexually violent and extreme in nature," said Gamble. "It also reflects the potential damaging impact that the possession of this material could have."
The law says that it is an offence to be in possession of an extreme pornographic image.
"An image is 'pornographic' if it is of such a nature that it must reasonably be assumed to have been produced solely or principally for the purpose of sexual arousal," says the law.
"An 'extreme image' is an image which is grossly offensive, disgusting or otherwise of an obscene character…and if it portrays, in an explicit and realistic way, any of the following –
(a) an act which threatens a person’s life,
(b) an act which results, or is likely to result, in serious injury to a person’s anus, breasts or genitals,
(c) an act which involves sexual interference with a human corpse, or
(d) a person performing an act of intercourse or oral sex with an animal (whether dead or alive),
and a reasonable person looking at the image would think that any such person or animal was real."
The Ministry of Justice has said that there are defences to prosecution under the law for those who do not ask for or keep images that are banned under the Act.
Guidance produced by the Ministry said that there is a defence available for "a person [who] was in possession of an extreme image but had not looked at it and therefore neither knew, nor had reason to suspect that it was an extreme pornographic image; this will cover those who are in possession of offending images but are unaware of the nature of the images for example, where a person is sent an electronic copy of an image which he saves without looking at it and which gave rise to no suspicion that it might be extreme pornography".
It said that there was also a defence for people who had been sent the message but did not ask for it, and who deleted it quickly. This is a defence even if the person looked at the image, it said.
Anyone found guilty under the Act could be jailed for three years and be ordered to pay an unlimited fine. They may also be placed on the sex offenders' register.