Nearly everyone in the City gets a bonus. (Well, I say "nearly everyone" - I mean, professionals, not cleaners and people working in canteens, I don't think.)
But the % of the bonus ranges quite a lot. If you work in, say, retail banking, or in investment banking, but far away from trading, your bonus might well be 10% or something of your annual salary, or less, depending on what sort of year you've had, and what sort of year the institution has had.
The closer you get to trading, and the higher your rank, the greater the possible %. Actual traders, or fund managers, can get multiples of their regular salary. The organisations like to pay people in bonuses, rather than in regular salary because a) they can scale back bonuses if they have a bad year, while you can't reduce a salary and b) they used to do all sorts of weird dodges to make the bonuses tax exempt. I think all those loopholes have been closed now, though.
Lots of City blokes lie to their partners about their bonuses - certainly I knew never to mention such things to people's wives.