By Dominic Casciani
BBC News home affairs
Counter-terror police have recorded a 37% increase in "suspicious reconnaissance" of potential targets in the first four months of 2007.
Counter-terror police are stopping and searching more people
Metropolitan Police commanders said the "undiminished" threat level justified the continued use of random stop-and-search powers.
But they accepted the reasons for almost 23,000 stops under anti-terror laws in London needed more explaining.
Campaigners say anti-terrorism stop and searches "criminalise" communities.
However, the Home Office may expand the powers yet further.
ANTI-TERRORISM STOPS AND SEARCHES
22,672 from Sept 05 to Oct 06
27 terrorism arrests
242 other arrests
16% of stops Asian
In February London police came under fire from their watchdog, the Metropolitan Police Authority, in a major report into the effect of counter-terrorism policing on the capital.
The watchdog found that the force's use of special anti-terror stop and search powers were doing "untold harm" to communities in the capital, in particularly Muslims.
Under Section 44 of the Terrorism Act 2000, police officers may randomly stop someone without reasonable suspicion, providing the area has been designated a likely target for an attack.
The power is currently in force across the whole of London.
But coming under fire for the use of the power, senior officers told the watchdog that the threat to the UK from terrorism remained "undiminished" - and that police had to use as broad a range of tools as possible.
Commander John McDowell, the Met's deputy national co-ordinator for counter-terrorism in the UK, said he agreed with analysis that the threat had worsened.
"There have been public pronouncements that the threat has grown in volume and I would concur with that," he said.
"Since 2005 we have seen an increase in activity and an increase in the gradient of the graph."
Commander McDowell said the first four months of 2007 had seen the police record a 37% increase in what it classed as suspicious reconnaissance - incidents that may be the first stage in planning an attack on the public.
He cautioned that this increase in reporting may be partly attributable to improved intelligence gathering as the security services expand counter-terrorism operations.
Assistant Commissioner Andy Hayman of the Met Police said the figure showed why officers were right to continue to use the Section 44 powers.
WHERE SEC 44 STOPS HAPPEN
26% Transport hubs
23% Outside Govt buildings, iconic sites, tourist attractions
13% Financial centres
Source: Metropolitan Police
While police could never be certain that a stop directly reduced the threat of a specific potential attack, he said it was important in a wider counter-terrorism context.
"What we do know is the mode of behaviour around a terrorist," he said. "If they feel that they could be stopped and searched under these powers, they could be prevented [from attacking]. What I don't know is how many are truly prevented."
Assistant Commissioner Hayman said that he accepted some of the criticisms of how the powers had been deployed - in particularly the lack of public information on who was being stopped.
He said the force would introduce a new rule book for officers involved in Section 44 stops - and the Met would also build a publicity campaign to explain to key communities why police believed the power was necessary.
Some officers were "unsure" of how the powers should be used, according to the Met's report into their use.
The defence of the powers came days after the Home Office said it was considering introducing a wider "stop and question" law.
The new power would give police an automatic right to stop and question anyone in the UK about suspected terrorism, building on the Section 44 power currently in force.
The proposal immediately drew fire from civil liberties groups and Muslim campaigners who predicted it would criminalise entire communities.