Overpayment of housing benefits

Hi,

I have a friend who is receving a small amount of housing benefit for the last 2 months. Recently he found a temporary job)2nd job) which might not last longer.
But he has not told the benefit department about this.
He is just waiting for another few weeks and inform the HB about the new changes as he is not sure if the job lasts that long.
He is ok to repay the overpayment.

1) If he doesnt inform the HB, can the HB find out that he is getting some extra money which should be declared?
2)Does HB time to time request the claimants to send the bank statements/salary slips to check about any info?


Regards
Thanks