A new official portrait of the king has been unveiled, created to hang in public buildings across the UK under an £8m government-funded scheme that an anti-monarchy campaign group has described as a “shameful waste of money”.

The Cabinet Office announced last year that it had set aside funds to offer every public body – local councils, courts, schools, police forces, and fire and rescue services – a free portrait of King Charles.

The photograph of the monarch in full regalia inside Windsor Castle was taken last year by Hugo Burnand, who also took the king and queen’s coronation portraits and their 2005 wedding photos.

Many public institutions displayed official portraits of Queen Elizabeth II, and “the offering of the new official portrait of King Charles III will enable organisations across the UK to carry on that tradition”, the Cabinet Office said.

“The accession of his majesty the king marked a new chapter in our national story,” said Oliver Dowden, the deputy prime minister. “Displaying this new portrait will serve as a reminder to us all of the example set by our ultimate public servant and I hope as many eligible organisations as possible will wish to continue this proud British tradition and honour our king’s reign.”

The Cabinet Office’s announcement last year was met with criticism amid complaints of shrinking budgets across Whitehall and local government. The anti-monarchy campaign group Republic called the initiative a “shameful waste of money”.

“At a time when a majority of local councils are raising taxes and cutting public services, when schools and hospitals are struggling, to spend even £1 on this nonsense would be £1 too much,” said Graham Smith, the chief executive of Republic.

He added: “The government has lost the plot if they think people want their money spent on pictures of Charles. They need to scrap this scheme and direct the money where it’s really needed.”

The official portrait depicts the king in his Royal Navy uniform as an admiral of the fleet, with his right hand resting on white gloves on an antique table and his left hand grasping a sword. He is standing in the royal residence’s grand corridor.

Public authorities can apply for a free portrait until 2 February, with delivery of the portraits expected to take place between February and April.