The threat of circulating “revenge porn” would be criminalised and the evidence threshold lowered to bring England and Wales in line with Scottish law, under changes to be proposed by a former Lib Dem cabinet minister.

The law south of the border has failed to keep pace with the rapid increase of the malicious exploitation of explicit or sexual images without their subject’s consent, according to former Scottish secretary Alistair Carmichael. He is to argue in the Commons in favour of amendments to criminalise not only the circulation of private sexual photographs and films without consent, but the threat of circulating them.

The proposed changes would also make it an offence to promote, solicit or profit knowingly from such private material. And the definition of private and sexual images will be expanded to include photographs and films of “breast and buttocks” rather than merely “exposed genitals”.

The Scottish parliament passed the offence of disclosing, or threatening to disclose, intimate images without consent as part of the abusive behaviour and sexual harm (Scotland) bill in March. Carmichael’s amendments will be voted on by MPs in the Commons when they come to debate the police and crime bill on Monday. They are designed to increase the number of successful prosecutions of the crime, which carries a jail term of up to two years and a fine.

Carmichael, who has already tabled an amendment proposing to give alleged victims anonymity, said: “In the last parliament we criminalised the awful act of revenge porn. One year on it is still a problem and convictions under the law remain abysmally low. We must act to do everything we can to empower victims to come forward.

“That is why I have tabled a raft of amendments to strengthen the law and ensure that victims aren’t left suffering in silence.

“I hope to get the support from MPs across the house and hope that the government agrees with me that more must be done to help and support victims of this horrific act.”

Figures released in April from 31 police forces after a freedom of information request revealed that most offences of revenge porn do not result in a criminal charge. There were 1,160 cases reported between April and December 2015 in England and Wales. Three of the alleged victims were just 11 years old. About 11% of the offences reported resulted in someone being charged. There were 82 prosecutions and 74 cautions were issued.

The College of Policing is also seeking to increase knowledge about the definitions and law in relation to revenge porn, which became a criminal offence in England and Wales in April 2015.

Last month it emerged that one man, Oliver Whiting, 36, from Eastbourne, received only a caution after five women came forward complaining they were victims. Campaigners also claim that the courts appear overly soft on the offence.

Last week the former girlfriend of an EastEnders actor was spared jail after posting a sexual video of him online when they separated.

Emilia Marcou, 40, and her friend Sarah McKenna, also 40, shared the explicit footage on Facebook. They earlier pleaded guilty to a “revenge porn” offence for publishing the video, which the actor, who cannot be named for legal reasons, had asked Marcou to delete after they broke up.

Marcou received an 18-week sentence suspended for 18 months, and McKenna a 12-week term suspended for 18 months, along with 12-month community orders, restraining orders and an £85 victim surcharge and an £80 government surcharge.