A police watchdog has warned officers that they should not be conducting stop and searches just because they smell cannabis on a suspect.
The report from Her Majesty's Inspectorate of Constabulary and Fire & Rescue Service (HMICFRS) said that more evidence was needed before carrying out a stop and search.
Officers can stop and search people if they have "reasonable grounds" to suspect they are carrying items such as drugs, weapons or stolen property.
However, the 'Police Legitimacy 2017' report states that the smell of cannabis on its own, with no other contributory factors, 'will not normally justify a search'.
The watchdog said that other factors should be taken into account before police stop someone and that there was an 'inconsistent' level of awareness of guidance around this.
It states: "The authorised professional practice (APP) sets out that the smell of cannabis on its own, with no other contributory factors, will not normally justify a search.
"More recent research has shown that the inclusion of the smell of cannabis in officers’ grounds for search did not increase the likelihood that a search for cannabis resulted in a criminal justice outcome.
"It concluded that a suspect’s behaviour should be more important than the smell of cannabis when deciding to conduct a search, because behaviour linked directly or indirectly to drugs increased the likelihood of a positive outcome.
"Our assessment of reasonable grounds found that 596 (7 per cent) of the 8,574 records assessed included only the smell of cannabis as the recorded grounds, suggesting inconsistency in the way the APP is being understood and applied."
Stop and search has repeatedly attracted controversy and reforms were introduced in 2014 by then home secretary Theresa May to ensure the tactic was used in a more targeted way.
Figures show this use of the powers has reduced sharply in recent years.
However, the controversial report has divided opinion between police officers with the chief constable of Merseyside Police disagreeing with the view.
Andy Cooke tweeted: "The guidance in my view is wrong and the law does not preclude it . Smell of cannabis is sufficient to stop search and I will continue to encourage my Officers to use it particularly on those criminals who are engaged in serious and organised crime."
Sheffield Heeley MP Louise Haigh tweeted: "The law is clear on this - smell of cannabis is reasonable grounds. @HMICFRS simply state that should look for other supporting factors as well."
The report also stated that police were less likely to find illegal substances on black people than white individuals when carrying out stop and searches for drugs.
HMICFRS described the disparity as "troubling".
The watchdog said: "It suggests that the use of stop and search on black people might be based on weaker grounds for suspicion than its use on white people, particularly in respect of drugs.
"There may be a number of reasons for these findings but, taken alongside the fact that black people are more than eight times more likely than white people to be stopped and searched, they require an explanation that the service is currently unable to provide."