If you get bonus and overtime and salary in the same month as others have said they'll assume that's your salary and tax you on it but return over next month or so.
Trouble you'll find is they'll deny they're wrong even when they are. I had them admit they had made a mistake and undercharged me by ~£600 which if they or your employer make a mistake and you've fully disclosed everything whoever makes the mistake eats it. After admitting they'd fucked up and undercharged me they still said I would have to pay - no way to fight it.
£41865 is the 40% threshold
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