Scotland Yard is to investigate a demonstration by Muslims outside Westminster Cathedral over Pope Benedict's remarks about Islam.
Around 100 people took part in Sunday's protest, which passed off peacefully without any arrests.
Since then the force has received a number of complaints from members of the public about the demonstration.
It is understood that some of the complaints relate to reported comments by the outspoken Islamic figure, Anjem Choudary - the former UK head of al-Muhajiroun.
Around 25 complaints have been received by the force.
Scotland Yard's Assistant Commissioner Tarique Ghaffur, the country's most senior Muslim officer, said: "We have a long history of facilitating lawful demonstration and are keen to continue dialogue with any group wishing to protest.
"However, what we will not allow is for people to attend demonstrations and break the law.
"Currently officers are looking at what took place (on Sunday), and also other publicly-made statements, with a view to ascertain if any criminal offences have been committed.
"We will always proportionately police all protest but equally will take decisive action where crime is committed."
The force had an officer at the demonstration taking still photographs.
