The anti-monarchy group Republic is planning a protest along the coronation procession route.

Organisers say this is their "biggest moment" with up to a thousand people taking part.

CEO of Republic, Graham Smith said: "This is the first time that a major royal event has been directly confronted with a protest of this size."

He believes the new monarch brings a new opportunity for republicans, with support and donations increasing since the King's accession to the throne.

"I think coronation day will be a moment, the biggest moment we've had. When they [the Royal Family] arrive, there are going to be millions and millions watching the coronation and so there will be millions watching us," he said.

Polling on the Royal Family is mixed, but a recent YouGov study found nearly two thirds of people either don't care, or care very little about the coronation.

The number of street parties planned is also significantly lower compared with last year's jubilee.

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The National Centre for Social Research runs a long-term study of attitudes to the monarchy, and it shows support is slipping.

The Centre's CEO, Guy Goodwin said: "In 1983, we were seeing about nine in 10 of us saying that it was really important that the Royal Family continued going forward. Today that figure is about just over half, around 55%."

If the figures continue falling, that's when Mr Goodwin says things could start to change.

"If you get close to that 50% approval rating... more and more questions will be asked around, you know, the funding and everything else associated with the monarchy potentially."

But even if public support is decreasing, political support is needed before any change could happen.

Law lecturer and constitutional expert, Dr Craig Prescott, says historically this hasn't happened.

"There have been lots of proposals to replace the royal prerogative or put it on a more modern, democratic basis. But once the political party gets into office they start to get focused on other more immediate matters… and these slightly arcane, constitutional questions get left by the wayside," he said.

When Gordon Brown first became prime minister he unveiled proposals reforming the constitution, but the global financial crash meant it never moved further.