Ed Miliband, Leader of the Opposition, described Andrew Mitchell, former Government Chief Whip, as "toast' a day or so ago (see video here).
This meaning of toast ("a person or thing that is defunct, dead, finished, in serious trouble, etc") entered the OED in 2002, and there are citations dating back to the 1980s. The first recorded use of the term is in the film Ghostbusters, where Bill Murray's character says "This chick is toast".
Toast appears as three noun headwords in the OED, and the above meaning appears under the first entry, which refers to toast meaning 'browned or grilled bread'. The word entered English from Old French, where toster meant "to roast or grill".
The second toast's first definition, which dates back to the early 18th century is "a lady who is named as the person to whom a company is requested to drink; often one who is the reigning belle of the season". Citations for this meaning include extracts from Jonathan Swift's and Fanny Burney's writings. Fifty years later the definition had widened to include men or anything else to which a toast might be drunk: "any person, male or female, whose health is proposed and drunk to; also any event, institution, or sentiment, in memory or in honour of which a company is requested to drink; also, the call or act of proposing such a health".
Originally, spiced bread warmed and browned at the fire was dropped into wine to give it flavour, and the OED thinks that it was for this reason that women came also to be called 'toasts'. A 1706 edition of the Tatler explained that during the reign of Charles II (1660-84) a belle was luxuriating in the health-giving waters in the spa of Bath, when a gentleman scooped up some of the water she was lying in, and drank it. Another gentleman, one who was rather more the worse for wear than the first chap, was supposed to have said that though he didn't like the liquor, he would have the toast. This story was put about by Joseph Addison, and I saw it on the website World Wide Words.
The OED talks only of ladies and belles being toasts - ie it is a positive word. However, if you have read more salacious books, journals and poems about the seedier side of 18th century London (which, I have to admit, I have), you will soon discover that when someone describes a woman as a 'toast', they are not speaking politely or genteelly at all, but are using 'toast' as a synonym of 'whore'. See for example Jonathan Swift's poem A Beautiful Young Nymph Going to Bed (the title is ironic), which begins:
Corinna, Pride of Drury-Lane,
For whom no Shepherd sighs in vain;
Never did Covent Garden boast
So bright a batter'd, strolling Toast;
You can read the whole poem here.
The third meaning of toast, which gets its own OED entry, dates back to the 1960s, is from the US and/or Caribbean and is "a type of long narrative poem recited extempore".