The ship going over a waterfall is a metaphor for the British economy, which is currently facing another recession. The group of people at the prow of the boat is striking public sector workers. One of them shouts, 'Everybody out!’ which is the traditional rallying cry for workers to 'down tools' and come out on strike (see below). There is, however, a play on words, as 'Everyone out!' could also be construed as a call for everyone to get out of the boat. Whichever way you look at it everyone is doomed!
During the 1970s in the UK this phrase ('Everybody out!') was synonymous with militant union activity. It was used when workers were called out on strike, although more often in drama and literature than in reality. The work that made the phrase known was the 1960s BBC sit-com 'The Rag Trade', where it became a catchphrase. The show was set in a clothing factory and virtually every episode included the shop-steward Paddy (Miriam Karlin) blowing a whistle and shouting "Everybody out!" [source: The Phrase Finder].