WINDSOR — On the eve of Prince Harry and Meghan Markle’s wedding, the picturesque town of Windsor has taken on the character of an impregnable fortress.

Every nook and cranny has been scoured and every imaginable security measure deployed to guarantee the safety of the royal couple and the tens of thousands of spectators set to flood the streets.

In a dress rehearsal Thursday for the journey Harry and Meghan will take through the town after the Windsor Castle ceremony, uniformed police -- some armed -- were out in force.

On one of the roads near Windsor Castle -- where Queen Elizabeth II often spends weekends -- officers used handheld torches to examine street lights, traffic lights, rubbish bins and manholes, anywhere along the road where a suspicious device could have been hidden.

"We’re just checking to make the wedding safe", one told AFP as his colleague led a sniffer dog on a hunt for hidden explosives.

Huge barriers have been hauled into place to prevent a vehicle attack and many roads are now closed in the town of 30,000 inhabitants, 30 kilometres (19 miles) west of London.

Number plates are also being automatically scanned and surveillance cameras have been deployed en masse.

Two months in the planning, the security measures are in line with the huge crowds expected.

The wedding is expected to attract around 100,000 spectators in Windsor itself, with at least 5,000 journalists, according to Thames Valley Police.

"A broad range of visible security measures are in place," a spokesman told AFP.

On D-day, train stations will be on high alert, vehicles will be inspected and visitors can expect to be searched.

No drones will be allowed to fly over the wedding zone.

"Things can go wrong whenever you have big crowds of people," said Chris Phillips, former head of Britain’s counter-terrorism security office.

"Terrorism is obviously the biggest threat."

"You have to treat everyone as a possible troublemaker or terrorist," said Phillips, who now runs security consultancy IPPSO.

Sent reeling after a series of attacks by the Islamic State group in 2017, Britain’s current terror threat level is "severe" -- the second highest it can possibly be -- indicating an attack is "highly likely".

But if "everyone can be a threat" then "everyone also can be a positive pair of eyes", said ex-police officer Phillips. — AFP