Welsh nationalist and folk singer reveals how extremist attempted to lure him into a fake plot to kill King Charles

He claims it was the work of an "agent provocateur" who he said looked like "a character from a B movie" before the 1969 investiture of Prince Charles.

Dafydd Iwan, who celebrated his 80th birthday over the summer, makes the startling revelation in his new autobiography, Dafydd Iwan: Still Singing Yma o Hyd, that is due to be launched on November 9.

He says the incident happened during the run-up to the investiture of the then Prince of Wales, now King Charles, at Caernarfon Castle at a time when his satirical song, "Carlo" (Charles) was high in the Welsh pop charts.

He said it came as the UK government at the time would use "unnecessarily heavy-handed methods to carry out their surveillance" when there was controversy surround the investiture, adding: "I experienced at first hand a rather pathetic attempt by an agent provocateur to put me in a great deal of trouble."

He recalled: “I arrived at a concert in Llanrwst to find the place crawling with police, and two of them approached me to say they’d received intelligence that someone was out to kill me, so they were there in numbers to give me protection.

"I was ushered into the marquee where the concert was to take place and shown into a small room in a corner of the tent. ‘We will be outside if you need us’, they told me.

"As I sat there, trying to come to terms with what I’d just heard, and getting the guitar ready for the stage, a man came in, looking like a character from a B movie, and said in a hushed voice that we’d met previously at a Plaid do in Holyhead. I’d never seen him before, and never saw him again.

"He said that he had very little time, so he wanted to come straight to the point. ‘We have a plan to assassinate the Prince, and you are the very man to help us’.

“I did not let him finish his sentence but told him to get out as quickly as his feet could take him and added that I didn’t ever want to see him again."

Dafydd Iwan was born in Brynaman, Carmarthenshire, in August 1943. One of four boys, his siblings include the late actor Huw Ceredig and the politician Alun Ffred Jones.

He spent most of his youth in Llanuwchllyn before attending the University of Wales, Cardiff, where he studied architecture.

His musical career started in the mid-1960s and before the decade was out he was receiving television coverage both for his music and for his political activities as a member of Cymdeithas yr Iaith.

He was imprisoned in 1970 for his refusal to pay fines for defacing English only road signs as part of the fight for Welsh language rights.

During his first spell in prison in Cardiff he met Cayo Evans, one time leader of the radical political group, the Free Wales Army, who acted as his "prison minder".

Dafydd Iwan was one of the founders of Cymdeithas Tai Gwynedd (Gwynedd Housing Association) in 1971 and was involved in other projects to provide homes for the local population in north-west Wales.

With fellow folk singer Huw Jones, he was also one of the founders of Recordiau Sain (Sain Records), now one of the main Welsh music labels with its own state-of-the-art recording studios in Llandwrog. He remains one of the company's directors.

For many years Dafydd Iwan was a Plaid Cymru councillor in Gwynedd and his long service to the Welsh language led to his being made an honorary member of the Gorsedd of Bards at the National Eisteddfod at Bangor in 1971.

His autobiography will be launched at the first of a series of celebratory gigs at Galeri Caernarfon.

Dafydd Iwan: Still Singing Yma o Hyd is published by Y Lolfa and can be bought from Amazon and Waterstones at a price of £9.99.