In this Adams' cartoon from The Telegraph, Angela Merkel and Nicolas Sarkozy are shown at the wheel of a steamroller which is going off the edge of a cliff. There is a horrified expression on their faces. David Cameron, in a little trolley, is being towed along behind the steamroller. His finger is raised as if he were trying to make himself heard.
The runaway steamroller is clearly meant to symbolize the euro (the euro sign is part of the roller). And going (or falling) off the edge of a cliff is a metaphor for disaster (see this earlier post). The cartoonist seems to be saying that Sarkozy and Merkel are powerless to save the euro, and that even if the UK is not part of the eurozone, its economic fate is tied (literally, in the cartoon) to that of the common currency.