ANTI-monarchy protesters have gathered in London for a major demonstration ahead of the State Opening of Parliament.

It is anticipated hundreds of people will join the event hosted by campaign group Republic outside the Houses of Parliament.

It is the first republican protest in London since the multiple arrests made at King Charles's coronation in May.

Twenty-one people were arrested on the day, but will face no further action after the Metropolitan Police said the Crown Prosecution Service had reviewed the evidence and concluded there was “no realistic prospect of conviction”.

Campaign group Republic said the message of the protest on Tuesday is simple: “Our campaign is about more than the monarch, it's about the place of the Crown in parliament and the ramshackle state of our constitution.”

READ MORE: LIVE: All the latest updates from the King's Speech

Protesters have been photographed outside the Palace of Westminster holding "Not My King" signs and flags which the monarch will pass as he makes his way to the House of Lords.

The National:

The King will deliver his first speech as monarch at the State Opening of Parliament on Tuesday which will see him read out the Government's planned legislation for the coming session. Charles deputised for the Queen last year.

It is likely this will be the final King's Speech before the General Election, which is expected next year. 

The event is filled with traditions that date as far back as the 17th century, often described by republicans as archaic and out of date.

The National: An anti-monarchy demonstration is in full swing in London

The King will travel to the event in the Diamond Jubilee State Coach as part of a procession of carriages. The crown and regalia are brought separately in their own carriage.

Republic managing director Graham Smith said: "It is just weird we continue with this pantomime that celebrates the worst, least democratic aspects of our political system."

King Charles is expected to arrive at the House of Lords between 11 and 11.30am.