Hi celj
Any annual bonus will be reported to Inland Revenue in an assessment period by your employer, Inland Revenue will inform DWP who will then calculate your entitlement for that assessment period.
I am not sure how you can get a surplus bonus, for some employees who are paid 4 weekly, every now and again you get 2 payments in one assessment period which will affect UC payments.
I would contact your local Welfare Rights Organisation who can take all your circumstances into consideration; you can find your local Welfare Rights Organisation to help you with advice by clicking on the link below and putting in your post code, it will then come up with a MAP with a list of agencies.
advicelocal.uk Gary