Which is more fuel efficient: 1.2 or 1.4 litre engine?

I always thought the lower the engine size, the more you save on fuel. But I've just read that the VW polo has 47.1mpg regardless of what size the engine is. I used to have a 1.4 which I liked but was thinking of getting a 1.2 for my next polo to save fuel. Can anyone explain to me what I should look for?... show more I always thought the lower the engine size, the more you save on fuel. But I've just read that the VW polo has 47.1mpg regardless of what size the engine is. I used to have a 1.4 which I liked but was thinking of getting a 1.2 for my next polo to save fuel.

Can anyone explain to me what I should look for? I've even read that the 1.9 litre diesel has 56.5 mpg. I'm confused!
Update: So if I have a choice between a 1.2 or 1.4 litre engine in a supermini volkswagen polo, should I go for the 1.4 litre (which I'd prefer) or will the 1.2 litre save fuel (which is the most important thing)
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