You are not allowed to work certain hours and continue to claim IB - without prior approval from the DSFA. You can claim an exemption from the Dept and ask them if you can work 15 hours per week or so - or otherwise engage in rehabilitative employment - but permission has to be got before you can engage in paid/non-paid work. When you are claiming you sign a declaration that you have not worked or been paid by your employer - and if you make a false statement you could be in serious trouble if you are found out.