Quartz. That was what we call a joke. Its humour is derived from the idea that Nick Clegg is known to break his promises, and relies as background upon the general shitness of the Lib-Dems. Its conceit is that if Nick Clagg announces that he intends to work to stop UKIP becoming "a Major Force in 100 Days", the the likely effect is the opposite. C/F Tuition Fees, the Mansion Tax, VAT etc, and of course the ineptitude of the AV Referendum, which worked out so well for the Lib-Dems*. Often humour is destroyed by signposting or overworking the punchline, as the laugh is obtained, in this case, by the speed with which the audience recognises and connects the juxtaposition of the relayed news story with the generally held perception, indeed, contemporary social convention, of Clegg as a promise-breaker with a background of ineptitude. The joke begins with a swear-word, which underlines the horror and frustration at hearing that in this instance an undesired outcome is in fact something Clegg has promised to do something about. "Oh no", the joke is saying, "that means the undesired outcome will become actuality!" Laughter is provoked by the coming together, then, of recognition, a release of tension, and, in small measure, a sense of the absurd, as the prospect of UKIP becoming a "major force" is, in the world-view of the joke, both horrifying and ridiculous.
hth
*sarcasm.