A bid for more power over housing in Wales made by the Welsh assembly has failed to gain Parliamentary approval.
The housing Legislative Competence Order (LCO) needed to be passed by Parliament before the general election.
It follows nearly three years of scrutiny and re-drafting of the LCO, which is the first stage in allowing the assembly to make its own laws.
The assembly government may not now be able to carry out policy aims around homelessness and affordable housing.
The Conservatives said they would not support it unless two clauses were removed - namely clauses to suspend the right to buy and one which they claimed could allow Gypsy sites to be built contrary to local decisions.
Following the decision, Jocelyn Davies, the assembly government's deputy housing minister, said it "was a huge disappointment and a huge blow to everyone in government and the housing sector in Wales who has worked on this for the last two years".
She told BBC Wales: "It would be very damaging if we had to start this process again once a new government has been elected."
She said the failure of the LCO to be passed before Parliament was dissolved highlighted the problem in trying to pass laws across two different electoral cycles - in Wales and in Parliament.
"I will do my very best to put my case forward and explain what this law will do for Wales to the next secretary of state for Wales," she added.
Welsh Labour leader and First Minister Carwyn Jones called the LCO "a crucial piece of legislation we needed to get passed".
"It's clear to everyone that Tories in Westminster have ridden roughshod over their colleagues in Wales, and are blocking progress of the new legislation based on their anti-devolution, right-wing ideology."
"The question now is whether local Tory candidates, like Simon Hart who went on the record saying the housing LCO was a good idea, will now distance himself from [Conservative shadow Wales Office minister] David Jones's blocking tactics."
"We know Simon Hart, like Tory AMs, previously supported Labour's housing policy, will he now stand up and be counted and condemn the actions of the Tory party in Westminster?"
Conservative shadow Welsh Secretary Cheryl Gillan said her party would support "efforts to tackle the issue of affordable housing" but accused Labour of "not being honest".
She said: "[Labour ministers] Peter Hain and Wayne David could have passed this LCO - including the provisions to which we object - at any time over the past few weeks using their Parliamentary majority.
"They have already done this with several other LCOs over the last few weeks. By delaying the passage of this LCO Labour has sought to play politics with social housing in a cruel, callous and calculating way, in an attempt to gain political advantage.
"They left this issue until the eleventh hour. We told Labour we would not oppose the LCO if they removed the elements we object to."
Liberal Democrat housing spokesman Peter Black said: "This outcome is further proof that the Tories do not understand devolution and do not care about Wales.
"Due to their intransigence and the incompetence of Labour and Plaid Cymru the assembly has once more been denied the opportunity to take important action to tackle the affordable housing crisis in Wales."
Mr Black said it took Labour and Plaid three years to get the LCO right and "by the time they delivered it was too late". But he said it could have been saved if Labour at Westminster had tabled it for debate in time, and if it had not fallen foul "of the political opportunism of the Tories".
Plaid Cymru Caernarfon MP Hywel Williams said neither the Tories nor Labour were "free from blame in allowing this situation to arise" and they "should be ashamed".
"When this LCO system came into being it was said that MPs would not be able to block the assembly from having powers on ideological or political grounds but these events have shown that the system is clearly not fit for purpose.
"And today we see the Tories - the same old 'nasty party' - scoring petty political points rather than helping those who are in need of government support."
Mr Williams said the Conservatives were involved in "political game playing", adding: "We urge them to put this to one side on such an important issue as people's homes, tackling the pressing issue of a shortage of affordable housing as well as housing support for the most vulnerable."