Mark Preston took the decision 'after much soul searching and with deep regret' after feeling that his position was unattainable following decisions taken by the ERYC leader Stephen Parnaby.
He refused to support the council's backing for the proposed fire reorganisation proposals, which included cuts locally, in the interests of Howden residents.
"The decision to support the fire brigade proposals, orchestrated by Mr Parnaby was at complete odds with the wider policy of the Conservative party, expressed by the shadow fire minister, supported by local Conservative MP's and against the better judgement of many councillors who reluctantly followed Mr Parnaby as a result of him using the party whip.
"This issue was a matter of life and death, and as such was surely a moral judgement according to each individual councillor's conscience," explained Mark.
He added that sanctions were taken against the only two councillors who spoke and voted at the council against the proposals, without permission, while his neighbouring Howdenshire and Snaith/Airmyn councillors were allowed a free vote.
"When councillors are expected to fall in line and vote at council or otherwise face sanctions and loss of chairmanships of any committees, then the use of such power needs to be questioned or local government will be tainted with accusations of cronyism and of members' self interest, being put before the interests of the public they are supposed to serve," explained Mark.
He added: "As such I can no longer serve under such a regime at County Hall, Beverley.
"My loyalty and commitment must be foremost to the residents of Howden and to the wider Conservative party."
Mark will remain a Conservative councillor on the ERYC, but believes that he will now have the opportunity to speak and vote in accordance with his 'moral judgement and resident interests, rather than have to obey the dubious judgements of others'.
Council leader Stephen Parnaby said that it was regrettable that Mark had taken this action.
He added: "I am sure with experience he would have a lot to offer both the council and Conservative Group.
"By now being outside the ruling group on the council he will not have the same influence and will find it difficult to be as effective on such a large council."