Well, you could read the story and find out, but to save you the trouble, it's a word that was coined by the BBC's political satire 'The Thick of It' to describe the totally chaotic mess that our politicians have got us into (omni= all, shambles - a mess). apparently the word has caught the popular imagination and is now in widespread use.
Incidentally, I've only seen a couple of episodes of 'The Thick of It', but oh my! What a load of shits they all are - they make all those awful people on 'Mad Men' seem quite nice.
MK