Police forces have made "disappointingly slow progress" in improving their use of stop and search powers, a watchdog has found.

Her Majesty's Inspectorate of Constabulary (HMIC) said too many police officers still did not understand the impact of the controversial practice, which affects a "disproportionate" number of black people and those from ethnic minorities.

The watchdog found there was a "surprising lack of interest" among police chiefs about the way strip searches are carried out, particularly on children and other vulnerable people.

There was also "no official record" of how police were conducting traffic stops after a survey by HMIC found black and ethnic minority drivers were more likely to be stopped.

HM Inspector of Constabulary Stephen Otter said: "Too many police leaders and officers still don't seem to understand the impact that the use of powers to stop and search people can have on the lives of many people, especially young people and those who are from black and minority ethnic backgrounds.

"This is disappointing because getting it wrong can lead to resentment, anger and, in time, a loss of trust in the police.

"It is well evidenced in lots of reports that one of the triggers for major disorder in this country is this power.

"Doreen Lawrence sits on our external reference group and it is difficult to look her in the face because of the lack of progress that's been made here."

A study by HMIC in 2013 found stop and search could have been used illegally one in four times.

Despite making 10 recommendations to improve police use of the powers, good progress had only been made in one area - improving the use of technology to record encounters, the watchdog said.

Mr Otter said there was a "lack of empathy" among police officers about the impact of stop and search.

"Ninety per cent of the time, there is no prosecution, they aren't criminals," he said.

"If you were black, it might be easier to empathise because it may have happened to you. It's much less likely to happen if you are white.

"Is it active discrimination? Is it racial profiling? There's a lot of research that suggests that's the case."

A survey of more than 12,000 police officers found that more than a third felt under pressure to carry out fewer stop and searches, while a quarter said they were under pressure to stop using the power entirely.

The study also found that a "small minority" of officers were arresting people in order to search them so they avoided the "increased scrutiny" of stop and search powers, HMIC said.

"Given that stop and search powers were introduced with the principle aim of avoiding unnecessary arrests, this concerns us gravely," HMIC said in its report.

"It could falsely indicate that stop and search encounters are reducing and almost certainly place more strain on the fragile relationships that the public have with the police when it comes to being stopped and searched."

The Home Office launched a best use of stop and search scheme last year, which was part of a range of measures aimed at slashing the overall use of the controversial practice.

It came after HMIC discovered 27% of stop and searches in 2013 did not contain reasonable grounds for suspicion, meaning more than 250,000 of the one million searches conducted each year could have been illegal.

In addition, black and minority ethnic (BME) members of the public were up to six times more likely to be searched than white people.

HMIC said that within three months police forces should require officers to record all searches involving the removal of more than an outer coat, jacket or gloves.

"We don't know how many children were stopped and strip searched," Mr Otter said.

"Engagement with the NGOs (non-governmental organisations) who listen to complaints about these things indicates from their view a level of concern that children are being strip searched. And when we talk about children we're talking about under 18 to quite a young level."

HMIC has also called for police to begin recording incidents when motorists are stopped over the next year after it found none of the 43 forces in England and Wales had conducted any reviews into whether the power was being used fairly and effectively.

A survey of 10,000 people - including 7,500 drivers - found 47% had been in a vehicle when it had been stopped by police.

The survey showed 7% to 8% of white drivers were stopped in the last two years, compared with 10% to 14% of black and ethnic minority drivers.

Prosecutions were more likely when white drivers were stopped, suggesting black and minority ethnic drivers were more likely to be stopped for no reason, HMIC said.

Deputy Chief Constable Adrian Hanstock, national policing lead for stop and search, said: "It is clear from today's report from HMIC that progress in improving the way the police service uses stop and search has not been good enough.

"We are committed to ensuring the police service focuses on carrying out these checks fairly and proportionately and that they are intelligence-led.

"We agree with HMIC's recommendation that there is an urgent need for national training requirements and a clearer definition about what constitutes fair use of stop and search powers. This will give both the public and police officers more confidence that we are using our powers correctly."

Home Secretary Theresa May said: "I have been clear that the police use of sensitive stop and search powers must be properly targeted, based on reasonable grounds and accountable to citizens and communities.

"While the number of stops and searches has fallen by a third under this Government, it is clear that police forces have failed to address many of the very serious issues raised by HMIC's inspection in 2013.

"If the stops and searches do not continue to fall, if the use of these powers does not become more targeted, and stop-to-arrests ratios do not improve, then I will not hesitate to bring in primary legislation to make it happen."