Among the hundreds of thousands of well-wishers who crowded the streets of London's Westminster area, police said they made 57 arrests in the royal wedding security zone.

According to the London Metropolitan Police, the arrests were related to a variety of offences including sexual assault, theft and possessing an offensive weapon.

"These include within and outside of the event footprint," the police said in an online release enumerating the offences.

The most common alleged offence was breach of the peace, which accounted for 25 of the arrests. Drunk and disorderly conduct was a distant second, with seven arrests.

Among those detained was a group of 10 people who were arrested close to Charing Cross train station. They were found in possession of a climbing helmet, dark-coloured clothing and anti-royalist placards.

In the days leading up to the wedding, more than 90 people had been banned from the security zone established in the historic area that includes Buckingham Palace, the Mall and Westminster Abbey.

Considering the size of the crowd -- which analysts expected to reach 1 million before day's end -- not to mention the intense global interest, any significant security breach would have been a blight on the celebrations. As a result, more than 5,000 police and security forces were dispatched to create a "ring of steel" around the wedding.

The operation comes at a reported cost of more than $31 million.

Ahead of the wedding, however, London police commander Christine Jones told reporters that the force has "no specific intelligence to suggest a threat to this event at this time."

Britain's terror alert level is nevertheless at its second-highest warning of "severe," which means an attack is highly likely.