A BLANKET ban on legal highs could force dealers onto the "dark web", a top police officer warned night.
The mind-altering substances – including 'hippy crack' and 'spice' – are being outlawed this week after being linked to several deaths.
But Commander Simon Bray said those determined to get hold of the drugs might turn to illicit websites on the dark web.
The new law will mean Britons can no longer buy legal highs "in a normal transaction" from a "head shop", the officer added.
Commander Bray of the National Police Chiefs Council added: "Clearly, there will be some movement onto the dark net.
"People find it lucrative to sell substances and where people are going to buy them.
"But of course, it is not going to be so easy for the average person to get hold of them."
Other experts have warned the ban will just drive use and sale of the drugs into the hands of criminal gangs.
Tejinder Reehal, who manages Scorpion, a shop that has sold legal highs, said: "We have seen it before with mushrooms and mcat.
"The most serious stuff will come off the market, but the milder stuff should be allowed to be sold."
Ministers and police say the ban, which will come into force on Thursday after several delays, will put some users off.
But a recent EU report concluded the relentless flood of new legal highs onto the market made controlling them all "unfeasible".
The EU Drug Markets Report said there were "no signs of a slowdown" in the development of new psychoactive substances.