If he gets 60 aweek in dole and declares to them he earnt £30 from window cleaning. They will give him £30. Or if he declares he earnt £60. They will pay him nothing for that week.
Or you can ask for self employment credit, this is for new start-ups. It works out at £50 aweek.
Working part-time or on low self employment income, you can still claim FULL housing support, council tax.