Police marksman, airport-style scanners and a plea for no confetti form part of the royal wedding’s security operation as more than 100,000 fans were estimated to have lined the royal wedding’s procession route.

A ring of steel has effectively been created around Windsor Castle as it plays host to Prince Harry and Meghan’s wedding, with the costs expected to run into the millions.

The Royal Borough of Windsor and Maidenhead estimated “just over” 100,000 fans watched the procession along the route, and the British Transport Police (BTP) reported that 20,000 passengers had streamed through the town’s stations by 9.40am.

Officers with sniper rifles were spotted on roofs around the town in what is one of the largest public events handled by Thames Valley Police (TVP).

In a bid to ward off vehicles being used as weapons, as seen in the terrorist atrocities committed on London and Westminster Bridges, metal barriers have been installed around the Berkshire town.

Armed officers, dog handlers and mounted police are also on the ground while, in the air, drones have been banned from flying over the estate and aircraft are restricted from flying below 2,500ft.

While confetti is not banned, TVP requested fans do not throw the “potential security risk” or other items throughout the day, particularly during the procession.

Along with the security scanners, visitors are being warned not to leave belongings unattended and that they could be subjected to inspections.

The operation was in progress months before the big day itself, and police were seen manning barricades outside the castle and sniffer dogs performing checks on Friday.

The US actress is a big draw for American fans as well as Britons and police estimated ahead of the event that more than 100,000 revellers would join festivities.

Almost every TVP officer is working on Saturday as Harry and Meghan’s 600 guests attend their wedding, 200 of which will celebrate at an evening reception hosted by the Prince of Wales at Frogmore House.

The security operation for the wedding of the Duke and Duchess of Cambridge cost police more than £6 million, according to figures revealed in April, with nearly half of that spent on overtime costs alone.

But the cost of this royal spectacle cannot yet be confirmed.

No arrests in relation to Windsor’s wedding celebrations had been made by 2pm, according to TVP and BTP.