4x30 = 120, in a 3 month period that's 120 hours for £835.90 or £6.96/hour. That doesn't seem obviously unreasonable, nor will the workers obviously displace other minimum wage type work.

There was an article in the economist recently (which I can't now find) which cited reasonably compelling evidence from some US states that forcing the unemployed to work is fairly effective at moving the long term unemployed back into work, in particular that a substantial number of those affected leave their compulsory job very quickly and move into a 'real' job.