10 February 2013 Last updated at 10:36

Tryweryn: 50 years since bombing of reservoir dam

'Remember Tryweryn' - the Welsh language graffiti recalling the drowning of Capel Celyn in 1965

It is 50 years since activists bombed a power transformer at one of the most controversial construction projects in modern Welsh history.

The Tryweryn reservoir saw the Meirionnydd village of Capel Celyn drowned to provide water for Liverpool.

Two activists were jailed after planting explosives at the site in February 1963.

On Saturday, more than 100 people gathered to mark the incident.

The issues surrounding the building of Tryweryn are widely seen as one of the sparks that ignited the Welsh language campaigns of the 1960s, and a focus for the growing devolution movement.

Seventy residents of Capel Celyn were forced to leave their homes, and in 1965 the village disappeared under the waters of the new lake.

It was not the first time a Welsh community had been displaced to provide water for English cities - the Vyrnwy and Elan Valleys had been flooded in the late 19th Century to create reservoirs serving Liverpool and Birmingham respectively, forcing similar numbers of people to relocate.

T Glynne Davies reports in 1967 from the shores of the new reservoir

But the Tryweryn project came at a time of growing Welsh nationalism and activism.

The reservoir for the then Liverpool Corporation was agreed in a bill passed by Parliament - although not a single Welsh MP voted in favour.

Political repercussions

In his book, The History of Wales, Prof John Davies noted: "Liverpool's ability to ignore that fact confirmed one of the central tenets of Plaid Cymru - that the national Welsh community, under the existing order, was wholly powerless."

Emyr Llewelyn was jailed for a year for the attack

Plaid Cymru's leader, Gwynfor Evans, had been at the forefront of the campaign to halt Tryweryn.

A year after Capel Celyn vanished, he became the party's very first MP, winning the Carmarthen by-election of 1966.

But back in 1963, while the reservoir dam in Cwm Tryweryn was still under construction, it was the actions of three young men that were making the headlines.

Aberystwyth student Emyr Llewelyn, farmer's son Owain Williams, and former RAF military policeman John Albert Jones, formed the shadowy group Mudiad Amddiffyn Cymru, the Movement for the Defence of Wales.

On the night of 9 February, they travelled through blizzard conditions to the construction site, and planted a 5lb (2.3kg) bomb at an electricity transformer powering the whole project.

But within a week of the explosion, Llewelyn was under arrest, after a police patrol noted the registration of the car hired by the student in Aberystwyth.

Llewelyn refused to name his co-conspirators, and was given a year-long jail term.

City apologises

However, on the day he was sentenced, Williams and Jones struck again, blowing up an electricity pylon at Gelliydan near Trawsfynydd in Gwynedd. This time they were both apprehended.

Liverpool's plans sparked widespread protests in the city and in Wales

Williams was given a one year sentence, while Jones received three years on probation.

However, the actions of the bombers merely delayed the reservoir project. It was finished and officially opened on 21 October 1965.

Exactly 40 years later, Liverpool City Council issued an apology for Tryweryn, stating: "We realise the hurt of 40 years ago when the Tryweryn Valley was transformed into a reservoir to help meet the water needs of Liverpool.

"For any insensitivity by our predecessor council at that time, we apologise and hope that the historic and sound relationship between Liverpool and Wales can be completely restored."

The reservoir, known as Llyn Celyn, can hold up to 71 million litres of water and continues to supply households in north west England via the river Dee. It also generates hydroelectric power and in summer is used for water sports.

Memories of the lost village of Capel Celyn are occasionally stirred during spells of dry weather, when some of its abandoned buildings become visible again when the water levels drop.

People gathered by the lake on the eve of the anniversary

The eve of the anniversary of the bombing was marked by a march and gathering of around 100 people on the banks of Llyn Celyn on Saturday, where speakers included one of the bombers, Owain Williams.

As well as being remembered as a significant moment in modern Welsh history, organisers of the commemoration claim the event has resonance today as controversial proposals for onshore wind farms divide opinion in rural Wales.