The government's independent reviewer of terrorism says special stop and search powers are being over-used.
Lord Carlile said the risks posed by terrorism, and its nature as a crime, meant special laws were needed to tackle the threat.
But he said the use of anti-terrorism stops could be halved without a risk to national security.
The Metropolitan Police have been criticised for the way the special stop-and-search powers have been used.
Earlier this year, the Metropolitan Police Authority, the watchdog for the capital's policing, said that there had been more than 22,600 stops and searches under Section 44 of the Terrorism Act 2000 - but only 27 arrests under the same act.
An officer can use this power without reasonable suspicion of a crime if the area where they are operating has been defined a likely target for terrorism.
ANTI-TERRORISM STOPS AND SEARCHES
22,672 from Sept 05 to Oct 06
27 terrorism arrests
242 other arrests
16% of stops Asian
Senior officers say the stops are key to policing potential bomb targets such as iconic buildings or tourist locations. Critics say the stops are creating tension across the capital, particularly among Muslims.
Lord Carlile said he accepted the case for special powers to combat terrorism.
But he said there was inconsistency among police chiefs over how to use Section 44 stops.
Writing in his annual report into the workings of terrorism legislation, Lord Carlile said the power was "perceived as a significant intrusion into personal liberties
"Whilst there is continuing work to improve the way in which section 44 is used, it is still used too much. It should never be used where there is an acceptable alternative under other powers.
"Although during my years as independent reviewer there has been a general increase in caution before utilising section 44, in my opinion its use could be halved from present levels without risk to national security or to the public."
Sharing of information
Lord Carlile also criticised police force special branches, saying there was a "continuing and regrettable problem about the exchange and sharing of information" about terrorism between different agencies.
He warned there were some "potentially vulnerable" ports of entry because of a shortage of customs officers.
He said: "HM Revenue and Customs, as its name implies, is led by the imperative of revenue collection. The discovery from personal baggage of a small piece of information potentially useful in detecting a terrorist cell is of far more value to the national interest than the discovery of a few thousand bootleg cigarettes.
"Current Revenue and Customs performance indicators give full value to the discovery of the cigarettes, and almost none to the small but potentially significant sliver of counterterrorism observational intelligence."