0245 GMT February 22, 2019
Of these, there were 126 fatalities in Scotland between 2015 and 2017.
Counterfeit Xanax bars with a street value of more than £1 million have been seized at UK ports and airports since 2016.
Border Force said its officers were "at the forefront of the fight to keep illegal drugs out of the country".
"We are taking a smarter approach to restricting the supply of drugs and are adapting our approach to reflect changes in criminal activity," it added.
Pfizer, the company that developed Xanax as a prescription drug, said it was ‘alarmed by the rise’ of counterfeit versions and that it "continued to work side-by-side with all law enforcement".
It added that Xanax was ‘subject to strict regulations" and "should only be used as prescribed by and under the supervision of a qualified healthcare practitioner".
Xanax, also known by the name alprazolam, is widely prescribed in the US to treat anxiety and panic attacks, and can be obtained on private prescription in the UK - though not through the National Health Services.
Counterfeit versions of the class C drug are often bought via the dark web, and mixed with other substances, which makes it extra dangerous.
There were 35 deaths reported in England and Wales between 2015 and 2018, figures provided by the Office for National Statistics show.
Between 2015 and 2017 — 43 people have died in Northern Ireland having misused Xanax with other drugs.
In 2018, some 340,000 counterfeit Xanax bars were seized at UK ports and airports, figures from Border Force figures and the Medicines and Healthcare products Regulatory Agency (MHRA) show.
The MHRA's head of enforcement, Alastair Jeffrey, said the key was raising awareness among the public and giving people "the knowledge that buying medicines outside the regulated supply chain is a really dangerous thing to do".
Northern Ireland's police service (PSNI) said counterfeit Xanax was the third most-seized drug there, accounting for 25 percent of the 113 deaths involving drugs recorded in 2018.
The PSNI's Detective Chief Inspector David Henderson said it had "more seizure incidents of [psychoactive drugs] benzo, which includes Xanax, than we do of heroin or ecstasy."
Some hospitals have been struggling to cope with overdoses involving the misuse of Xanax.
NHS Grampian in Aberdeen issued a warning of the dangers in 2018, having recorded 29 deaths involving the drug the year before.
The Scottish government said it was "increasing awareness of the health-related dangers of misusing prescription drugs… and addressing the underlying factors".