Each council works out eligibility in a different way, so you will need to check with your council if you will still be eligible, or use a benefits calculator such as:
 
http://www.entitledto.co.uk
 
‘Clawback’ of earnings is usually at a very high rate – often 75% to 80%, so be aware that if you are receiving some Council Tax Support, you may lose up to 80% of the value of your bonus (if this is more than the value of your annual Council Tax Support).
 
If your Council Tax Support is reduced, you may have to repay any Council Tax Support you have received since April.
 
How to Report: Report any change of income immediately to your Council’s Council Tax Support department.