A topless protester ran past the crowd at the Windsor Castle and shouted "save the planet" after a minutes silence was held for Prince Philip, the Duke of Edinburgh and husband of Queen Elizabeth II, who is being laid to rest at the palace on Saturday in a small family affair due to the Covid-19 restrictions.
The woman appeared to try and break through the security barriers, the DPA news agency reported.
Others at the scene said she jumped onto a nearby statue of Queen Victoria. The protester was placed in handcuff.
Earlier, the ceremonial royal funeral of Prince Philip was held at the Windsor Castle. More than 730 members of the armed forces took part in the event but there was a limit of 30 mourners at St George's Chapel, under Covid rules.
The Prince's coffin was carried the short distance to St George's Chapel on a modified Land Rover, which the duke himself helped to design.
The funeral procession from the castle to the chapel was headed by the Band of the Grenadier Guards, the Major General's party, and military service chiefs.
Vice Admiral Sir Timothy Laurence and the Earl of Snowdon also walked behind the coffin, trailed by members of the duke's household staff.
The Queen, 94, travelled with a lady-in-waiting in the state Bentley at the end of the procession. Following the procession, a Royal Marines bearer party carried the coffin into the service.
A ceremonial gun fire at nine locations across the UK, and in Gibraltar, marked the start and end of the national minute's silence. Heathrow Airport said no planes would land or take off for six minutes to coincide with the silence and all major sporting events have been rescheduled to avoid a clash with the funeral.
The funeral service was conducted by the Dean of Windsor, with the Archbishop of Canterbury pronouncing the blessing.