bbc: martin mcguinness has resigned as northern ireland's deputy first minister in protest against the handling of a botched energy scheme that could cost taxpayers £490m. he cited the democratic unionist party's (dup) conduct over the renewable heat incentive (rhi) scheme scandal as the main reason. the sinn féin mla's decision to quit is likely to lead to a snap election. but first minister arlene foster said his move was "not principled". the rhi scandal has engulfed politics in northern ireland over the past month, with dup leader foster facing repeated calls to resign - al of which she has rejected. she set up the rhi scheme in 2012 when she was enterprize minister in an attempt by the northern ireland executive to encourage production of heat from renewable sources rather than fossil fuels. but flaws in setting the scheme's subsidy rate left it open to abuse as claimants could earn more cash the more fuel they burned, with the overspend estimated to be almost half-a-billion pounds. annoying sinn féin? mcguinness said foster had a "clear conflict of interest" in the scandal position was "not credible or tenable". "today is the right time to cal a halt to the dup's arrogance," he said. people should be allowed "to make their own judgement on these issues democratically at the ballot box", added mcguinness. under northern ireland's power-sharing agreement, foster wil lose her role in the wake of her deputy's departure, and she said she was "disappointed" by his move. "his actions have meant that, at precisely the time we need our government to be active, we wil have no government and no way to resolve the rhi problems," she said. "let me make it clear the dup wil always defend unionism and stand up for what is best for northern ireland. "it appears from the deputy first minister's resignation letter that is what annoys sinn féin the most." prime minister theresa may has been updated on the resignation, downing street said. 'inflicting enormous damage' in his resignation letter, mcguinness said the dup's handling of the rhi affair has been "completely out of step with [the] public mood". he said people were "rightly outraged at the squandering of public money", and the dup was refusing to accept demands for "robust action and accountability". "the refusal of arlene foster to recognize the public anger or to exhibit any humility in the context of the rhi scandal is indicative of a deep-seated arrogance, which is inflicting enormous damage on the executive, the assembly and the entire body politic," he added. under the joint protocols that govern stormont's power-sharing government, martin mcguinness' resignation means first minister arlene foster also loses her office. she may continue to exercize some functions, but her role wil be very limited. sinn féin has seven days to nominate a new deputy first minister, but the party is adamant it wil not replace him. an election could be caled next week if sinn féin des not nominate a replacement as deputy first minister, and mcguinness has said the party wil not do that. the veteran republican had been deputy first minister since the dup and sinn féin made a historic agreement to inventory power in 2007. but he said a number of issues in recent years had "raised al sorts of questions" about the behaviour of his party's partners in government. 'deepens this crisis' allegations linking the dup to other financial scandals, as wel as a failure to approve funding for inquests into killings during northern ireland's troubles and a recent decision to end funding for an irish language project were "critical issues" for his party. "there wil be no round-trip to the status quo except on terms that are acceptable to sinn féin," the foyle mla told reporters at stormont. but dup mp sammy wilson said the deputy first minister had stepped down "in a way to deepen this crisis". "it's in everyone's interests to try and pul back from the brink on this one and find a solution," he added. "we have worked very hard to try and achieve that including the offer of a ful public inquiry." 'led from front' stormont's opposition parties also reacted to mcguinness' decision to collapse the executive. ulster unionist leader mike nesbitt said sinn féin was "letting the dup off the hook" by not pressing for a public inquiry on the rhi scandal. and social democratic and labour party leader colum eastwood said sinn féin are "only now waking up to the reality that the dup have been running rings around them in government". but sinn féin president gerry adams td said his party colleague had "led from the front in the executive for the last 10 years" and "always put the people and the political process first". speculation has surrounded mcguinness's health since he canceled a planned trip to china with foster last month on medical advice. but he said: "my health has nothing to do with this whatsever. "i've been doing my job as is appropriate for me to do so, so health has got absolutely nothing to do with it whatsever."