'Not My King' protesters unfurl flags and shout anti-monarchy slogans on Coronation route

Police were seen bundling anti-monarchists into the back of police vans and confiscating 'Not My King' banners after hundreds of protesters turned up to stage a demonstration of the coronation route.

Republic's chief executive Graham Smith was arrested by police, hours before the Coronation began as his supporters claimed he was detained for carrying a megaphone, which is banned.

The group's spokesman Luke confirmed the arrest and told Mail Online: ‘We have been told it was because he was carrying a megaphone. But the police had not warned us before that we weren’t allowed to have them.

‘I understand that five other people from a movement have also been detained.’

Up to 2,000 people are expected to join peaceful 'Not My King' protests in Trafalgar Square and along the coronation procession route today. 

Police were seen scouring vans with hundreds of Not My King banners 

A protester holding up a 'Not My King' sign as thousands are expected to demonstrate on the Mall today 

It comes amid fears eco-zealots are plotting a graffiti attack on a monument in The Mall during the Coronation of King Charles, as police vow hardline action against such tactics.

While Just Stop Oil has not announced any planned protests at the King's coronation, it did not rule out the possibility and yesterday said it could 'neither confirm nor deny' it would be undertaking action.

A 'ring of steel' has been placed around the capital with 11,500 police officers on duty and a further 10,000 military personnel taking part in the ceremony, in what is set to be the biggest security operation in British history. 

Anti-monarchists unfurled huge yellow 'Not My King' flags have joined the thousands of royal super-fans and well-wishers on the Mall for King Charles III's coronation.

A record 11,500 police officers - a large number of them armed - will guard London this weekend in what is set to be the biggest security operation in British history

 'Not My King' demonstrators were heard shouting anti-monarchy slogans as they joined the thousands of people who had assembled on the coronation route in central London this morning.

Mr Smith was arrested outside the Chandos pub, near Charing Cross rail station as he made his way to greet his colleagues in Trafalgar Square.

Police also searched a van which had hundreds of placards, but did not confiscate them.

On the Mall, Republic protesters were seen crammed into one corner Trafalgar Square as a spokesman for the group, who would only give his first name of Luke, said: ‘We are here to stay at her opposition to the monarchy.

'We don’t want them and we don’t need them and they don’t represent the entire population. We should have an elected head of state.

'It is not a good system with good values that we have at the moment.'

He said his organisation had chosen the coronation as it was an important event, which would attract attention from all over the world and help spread their message. 

Republicans who have gathered in Trafalgar Square for a Not My King protest are currently outnumbered by royal fans.

One royal fan, Chris Riley, 55, a contracts manager from Nottingham, told MailOnline: ’I love the King. I hope it’s the most glorious day for him and the country. ‘I’m a bit disappointed that there are people here with banners against the monarchy, which is a bit distasteful.’

A protester waving a 'Not My King' flag at Trafalgar Square, central London, on Saturday 

Anti-monarchists unfurl huge yellow flags on the Mall on the day of King Charles' coronation

Tim Constantinou, 54, from Stoke on Trent and a former Army corporal, said: ‘ This is a momentous occasion and one I had to be at.

‘I have always been impressed with Charles and I met him in 1991 when I came back from the Gulf war.

‘We had lost a few people from our regiment and he knew their names and was very knowledgeable about the regiment. He has time for people and a genuine interest. ‘I think he will be a wonderful King and unite the country for many, many years to come.’

Susan Williams,19, from Castle Bromwich said: ‘ I think the King is great. But I’m more in love with William and Harry and Kate is just incredible with her style.

'I hope Charles has a very long time as King, but I think William will be really cool when he takes over.'

Metropolitan Police marksmen take up position ahead of the coronation

Huge crowds have already gathered in central London ahead of the King's coronation

Earlier this week, Republic said 'it will not be deterred' after receiving a 'passive aggressive' letter from the Home Office warning them against plans to protest at the King's coronation.

The group has slammed the Home Office for the official warning letter which they 'interpreted as a passive/aggressive intimidation of a legitimate protest group'. 

The letter, sent by the Home Office's Police Powers Unit, set out new offences under the Public Order Bill which was given Royal assent by the monarch yesterday.

Under new legislation, protesters blocking key infrastructure such as roads, airports and railways can face 12 months behind bars.

Anyone found 'locking on' or gluing themselves to buildings or objects could get six months in jail and face an unlimited fine. 

A police officer standing guard as thousands of people stand along the procession route ahead of the King's coronation

A protester seen wearing a 'Not My King' beanie hat

A protester waves a 'Not My King' placard as thousands gather in central London for the coronation

Police can also stop and search anyone they suspect is planning to cause disruption under measures which came into force today - ahead of the coronation on May 6. 

The Home Office has contacted a number of protest groups to notify them of new offences which may affect them.

But Graham Smith, the chief executive of Republic, said its campaign around the coronation will proceed as planned.

Mr Smith said it is 'very odd' the letter came from the Home Office and described it as 'intimidatory'. 

Police seen speaking to Just Stop Oil protesters on May 3, days before King Charles' coronation

He said: 'We have had two meetings with the Met police, and numerous phone conversations.

'They have repeatedly said they have no concerns about Republic's plans. It is a mystery why the Home Office thought it was necessary to send us an anonymous letter that could be interpreted as intimidation.'

'Republic will not be deterred and we will be protesting on Trafalgar Square and along the route of the coronation procession on Saturday.

'It is telling that Charles, who has had no problem speaking up on various issues, has chosen not to defend democratic rights when they are being threatened in his name. Perhaps he might make it clear that he believes in the right to protest.'

As a huge security operation got under way, protesters planning to disrupt the coronation were warned that they could be shot by police if they run out towards a carriage just in case they are carrying a bomb.

HMS Diamond, a Type 45 destroyer, will stand guard on the Thames to shield the King

Former royal protection officer Simon Morgan, now director of operations at security firm Trojan Consultancy, said: 'It's an armed policing operation because of the threat that the UK faces, the threat that the royal family faces, dignitaries that are attending. So we have to be very careful.

'Somebody that's going to run out in front of the carriage, fiddling with something in their rucksack, who's to say that's not an IED rather than a banner that's just going to be unfolded.

'These demonstrators have to be very careful as to the environment that they're going into, the police are acutely aware of it.' 

Facial recognition technology will also be deployed to flag to police any individuals on watch lists or who have outstanding warrants. 

While HMS Diamond, a Type 45 destroyer capable of tracking drones from 250 miles away, will also stand guard on the Thames over the King's Coronation weekend.