A sex offender could not be prosecuted for an alleged sex assault on a young child because his victim said it took place on a truck travelling between Scotland and England, MSPs have heard.

Victims' campaigners have urged Holyrood to close a loophole that prevents prosecutors punishing sex offenders who prey on their victims across UK borders.

Last week, Holyrood's Justice Committee heard an offender had to be prosecuted twice because he took covert photos of a woman taking a shower in England but stored them in Scotland.

Today, the committee heard of another cross-border loophole which saw a charge against a man convicted of abusing his stepdaughter dropped because the child could not say which part of the country she was in.

The Abusive Behaviour and Sexual Harm Bill is designed to address cross-border difficulties but campaigners fear it may still contain loopholes.

The Bill is also designed to criminalise "revenge porn", images taken consensually in a relationship but later distributed following a break-up.

However, victims' campaigners have called for the definition to be extended to include intimate texts and audio.

They also called for "creep shots" such as covert snaps up skirts or down blouses to be criminalised in the Bill amid fears that existing voyeurism laws may not criminalise the distribution of such images.

Nicola Merrin, policy officer at Victim Support Scotland, said: "Quite a few years ago we supported a lady whose daughter had disclosed sexual abuse over a period of years since an early age by her stepfather.

"The stepfather had a truck and some of the abuse happened on this truck that was travelling between Scotland and England.

"The offender was prosecuted for this crime but for the incident that happened on the truck, because the girl couldn't disclose where that happened because she didn't know where she was, the procurator fiscal said: 'We cannot prosecute this specific offence - we can look at everything else but not this specific offence'.

"That was quite distressing and obviously confusing to the mother and the daughter."

Ms Merrin said she understands the Bill is designed to address such gaps but raised concerns about evidence submitted by Glasgow University law professor James Chalmers, who suggested the Bill could contain a loophole for people whose residence switches between Scotland and England.

She said: "Professor Chalmers said he doesn't think it does satisfactorily addresses the issue of uncertainty and we would like the Bill and the committee to ensure that that is addressed.

"Regardless of where that happens, we would like you to make sure it can be prosecuted."

Labour MSP Margaret McCulloch asked if "upskirting and down-blousing", pictures which are normally taken without consent, should be criminalised in the Bill.

Louise Johnson, national worker on legal issues at Scottish Women's Aid, said: "These used to be referred to as 'creep shots'.

"I don't know if that was a description of the person who took them, or of the way the person was crept up on. But it's interesting to see that these might not be covered.

"The original offence was voyeurism, which might cover the taking but not necessarily the distribution, so we really want to ensure that all angles are covered because it would be terrible to get this far and find out there is a gap."