A leading human rights organisation says plans to let door staff at town centre pubs and clubs target "potential offenders" with an invisible liquid could prove discriminatory.

Kent Police is distributing canisters of the so-called 'SmartTag' spray to venues in Ashford and it says the liquid - which is invisible to the naked eye - contains a "long-lasting forensic code" which can link an individual to a certain place and time when it was deployed.

This marks the first time such technology, which police say has been used successfully elsewhere in the country, has been used on the streets of Kent.

But Liberty, the UK’s largest civil rights organisation, fears black and ethnic minority customers could be unfairly impacted by the scheme.

The group's policy and campaigns manager, Emmanuelle Andrews, said: "We all want to be safe in our local areas but this scheme tagging potential offenders will be rife for misuse and abuse, and will likely be disproportionately used against communities of colour and black people, who already face overbearing and oppressive police practices.

"This tool is being rolled out to security personnel with no evidence to suggest it would work, without proper scrutiny, and risks normalising increasing surveillance in our everyday lives.

"Rather than relying on surveillance and punishment, we should instead be focusing on measures that have fairness and human rights at their heart."

In Ashford Victoria, the ward which includes the town centre, there were 299 crimes reported in November, 85 of which were violence or sexual offences and 52 which were antisocial behaviour.

During the three months July to September, there were 99 instances of stop and search being used in the borough - disproportionately affecting black and ethnic minority people.

Door staff at pubs and bars will be able to use UV torches to identify those who have been sprayed with the tagging formula at other businesses so as to prevent them from entering their own premises.

Police officers can also use the liquid's unique coding to assist in their investigations into reported crimes.

The SmartTag initiative, paid for by the Safer Streets Fund, was introduced to a first Ashford venue in mid-December and police say it is hoped it will be extended to other locations around the town.

All venues with Security Industry Authority (SIA) accredited staff can apply to be part of the scheme, which is supported by Ashford Borough Council (ABC) and Ashford Partnership Against Crime (APAC).

Responding to Liberty's concerns about the use of the technology, Ashford District Commander Chief Inspector Nick Sparkes said posters will be up to alert revellers to the scheme.

He said: "Previous trials in other areas of the country have demonstrated that security staff equipped with SmartTag were able to calm down potentially violent situations, in most cases without ever having to use the spray itself.

"It has also assisted in a reduction in crime and increase in successful prosecutions.

"However, in cases where an offence has been committed, it provides an extra option, placing specific suspects in a certain place at a certain time, while keeping staff and the public safe.

"The liquid itself is harmless and invisible and any use of the technology in evidence will be subject to the same scrutiny as that provided for any other criminal prosecution.

"To ensure that security staff are properly trained in its correct use, access to SmartTag is restricted to Security Industry Authority (SIA) accredited staff, who have passed an online training course.

"Any use will be integrated into existing robust local partnership licensing reviews and renewals.

"Posters making customers aware that the scheme is in use are placed in all premises where staff have been provided with the spray."