The Govt. have settled on a weekly figure upon which it deems it is possible for a person/family to exist.
*Any* additional income, except where specifically stated in the statute, ought to be brought to the attention of the Benefits Agency.
If the BA then decide that this additional income does impact on the 'allowance' they will make the necessary adjustment, but they need to be informed about it, in any case, as part of the obligations the recipient has to be scrupulous with their dealings with DWP in return for receiving any benefit.