The Encyclopaedia Galactica has this to say on the subject of resignation:
Resignation is depart from job, or post, as posh people call job, and fuck-off quick, generally with immediate effect.
To tender resignation is to announce immediate departure, generally after some episode or episodes of bad behavious incompatible with the post which the postholder holds, so to speak, or held. Like stealing. And stealing in concert with one's equally post-holding husband. Or Mackay.
Mackay Trusted adviser to a man who trusts his advice, until he gets caught thieving and then has to be sacked, with gratitude for all the thieving advice.
standing down at next election means to get off Jock-free and is not resignation in accepted sense of word, especially since would have lost election anyway.
David Cameron means two-faced, career bully, mealymouth arsehole: eg thieving cow is not resigning in a year's time because of wrongdoing now, Oh, fuck me, no, it is because of media pressure which is intolerable and she has much to offer in future, although not as Treasurer. Which I fully respect.