Welsh Secretary Alun Cairns has told MPs that he would "really like" the Swansea tidal lagoon energy project to go ahead.
Speculation has been rife that the £1.3 billion scheme will be pulled by Business Secretary Greg Clark on cost grounds.
At Welsh questions Mr Cairns was repeatedly pressed to support the scheme and was told by Plaid Cymru's business spokesman Jonathan Edwards that he would be remembered as the "Grim Reaper of Welsh politics" if it did not go ahead.
Tidal Lagoon Power says it would need subsidies similar to those for new nuclear power to build the sea-wall which uses turbines to generate low-carbon electricity from the tides in Swansea Bay.
The company says the scheme, backed as a "pathfinder" project to develop the tidal technology by an independent review for the Government last year, would add just 30p to the average household energy bill per year.
Mr Edwards, speaking in the Commons, said: "The Secretary of State is fast becoming the Grim Reaper of Welsh politics, the bearer of bad news. When he pulls the plug on the lagoon there will be huge public anger in Wales.
"Isn't it the reality that many people back in the motherland will be left asking not only what's the point of the current Secretary of State for Wales but what's the point of having a colonial secretary at all?"
Mr Cairns said he was disappointed with the comment, adding: "I would hope that he would recognise the fair funding settlement that we've got for Wales, something the Labour Party ignored for 13 years.
"The seven tolls announcement, the city and growth deals that we've got, Swansea is a £1.3 billion scheme, the Cardiff scheme is the biggest in the UK and I hope that demonstrates the value a Secretary of State for Wales can bring."
Labour MP Carolyn Harris (Swansea East) later added: "Electrification - we haven't had it, tidal lagoon - if the FT is to be believed we're not gonna have it.
"When is the Secretary of State gonna start speaking up for the people of Wales."
Mr Cairns said no announcement has been made on the lagoon, adding: "We're doing anything and everything possible to try to make this fit."
In answer to a later question, Mr Cairns said: "I would really like the tidal lagoon to go ahead but of course it must prove to be of value for money."