By Andrew Bomford BBC Radio 4's PM programme

Official apology over Tryweryn

"I think that really riled people," remembered Alun Ffred Jones, who was a 15-year-old boy at the time.

"These people had drowned this village and driven people from their homes, and they were suddenly arriving to have a tea party."

"Suddenly the crowd broke over the dam and ran towards the tents where the speeches were going to be made. They started shouting, hauling on the ropes, banging, and the whole thing descended into a complete fiasco," he said,

"They had to go away without their tea and cakes."

Alun Ffred Jones is now the Plaid Cymru National Assembly member for Caernarfon.

Tryweryn memorial chapel by the shore of the reservoir

The ruined opening ceremony was the culmination of nine years of protest.

With the backing of English MP's, Liverpool City Council had driven through a Parliamentary bill approving the flooding of Tryweryn to create a reservoir providing water to the city.

It involved the destruction of a village called Capel Celyn, and the forced removal of about 70 people.

Every Welsh MP except one had voted against it, and gradually the Welsh people realised that when it came to a conflict with their bigger English neighbour, they had no control over their destiny.

The demonstrations spawned into a wider Welsh nationalist movement, and created support for Plaid Cymru which at the time was not much more than a Welsh language and cultural organisation. It soon gained its first political representation.

"It was born out of frustration," Alun Ffred Jones added. "The frustration that they simply had been unable to do anything about what was happening to them."

The authorities had used terrorism to get rid of the locals from their houses. Explosives were used to blow up their homes. So who were the terrorists? Owian Williams

Sometimes frustration boiled over into violence.

"We went out and destroyed the transformer which supplied electricity to the dam by using explosives," said Owain Williams, who is now a county councillor.

He got together with two friends and carried out several attacks during the construction of the dam and was eventually arrested and jailed for a year. He regards himself as a freedom fighter, not a terrorist.

"The authorities had used terrorism to get rid of the locals from their houses. Explosives were used to blow up their homes. So who were the terrorists?" he said.

Sculptor John Meirion Morris with a smaller version of the proposed memorial

"I believe that was the turning point in the battle to gain self respect as a nation. It rekindled national reawakening within Wales."

It is a hurt that has now prompted an official apology from the city of Liverpool.

Mike Storey, the leader of Liverpool City Council, has used the 40th anniversary to say sorry for what happened.

"It is right and proper at times to say sorry for past failings of our leaders, " he said, "I think saying sorry and apologising for previous acts is perhaps something we should do more often."

This recognition is something for the people of Wales, but many of those directly affected are not impressed.

"I think nothing of it, it is just away to say goodbye and sweep it all under the carpet," said Betty Watkin-Hughes, whose family was forcibly moved from Capel Celyn.

"They can keep their apology and start doing what's right for the people who are left."

Money is now being raised by public subscription to build an eight metre high memorial in bronze to be placed by the lake. It would be made by the Welsh sculptor John Meirion Morris and looks like a mythical bird rising out of the water.

"It is a bird and a choir, but a choir singing protest songs - even shouting protest songs," he said, "There's a mass of faces there, angry and determined."

Liverpool City Council is considering making a donation. "I would be quite happy for the city to make a contribution," said Mr Storey, "But I equally feel that the public should get behind it."

Tryweryn is a place with a rich history, and not just of Welsh nationalism.

In 1916, at Frongoch in the valley, 1,800 Irishmen, including the republican leader Michael Collins, were interned there after the Dublin uprising.

The Irish called it the University of Revolution, and it played a big part in the evolution of the republican movement in Ireland.