The protesters landed on the island on Friday

The 12 members of the Trident Ploughshares group set up a peace camp on Drake's Island last Friday and declared it a nuclear-free state.

The group said campaigners intended to stay as long as they could.

Island owner Dan McCauley has said he is unhappy about the invasion, but police say they have not yet received any complaints.

Drake's Island First fortifications built on the island in 1549 In 1583 Sir Francis Drake was made governor of the tiny island In the late 16th century, barracks for 300 men were built on the island in case of a Spanish invasion After the Civil War, the island became a state prison for 25 years

The island's new civic head is female protester Michal Lovejoy, a group spokesman said.

Ms Lovejoy has penned a letter, also signed by the mayors of Nagasaki and Hiroshima, calling on civic heads worldwide to come out against war and for peace.

Two of the protesters travelled to the mainland to deliver a copy of the letter to Plymouth's civic head's office on Monday.

The 6.5-acre island, which lies half a mile off Plymouth's waterfront, contains derelict military barracks and buildings from the Napoleonic era.

The group targeted Plymouth because the local dockyard is the base for Trident submarine refits.

Dan McCauley has owned the island since 1995

The group and their supporters claim the UK has breached the Nuclear Non-Proliferation Treaty by refitting nuclear-powered and nuclear armed Trident submarines at Devonport Dockyard.

Some of the campaigners are to leave to set up a disarmament camp outside the dockyard from 19 to 22 May.

The group also plans to blockade the dockyard on the morning of 20 May.

Former Plymouth Argyle FC chairman Dan McCauley bought the island for an undisclosed sum from the Crown Estate in 1995.

On hearing about the invasion, Mr McCauley said he had no sympathy with the group's cause, calling it a "security risk".

Devon and Cornwall Police said: "This land was sold by the MoD to a private landowner some time ago, and is therefore under the jurisdiction of this force.