Back to Work Benefit

I am currently receiving ESA and doing casual work 14 hrs a week under the Permitted Work rules for the last 8 months. In 4 months time the 52 week period allowed expires and I will have to consider stopping work altogether and just claim ESA or carry on working without the benefit. I may be able to increase the hours to just over 16 a week but it would still only be on a casual basis as until I am strong enough there is no permanent work available. Would I then be able to come off the ESA and claim the "Back to Work" benefit of £40 a week to top up the income. Also if I can go down these lines and I can;t cope with the work for more hours because of my illness or the casual work ends, will I then be able to go back on ESA easily? Has anyone had similar situation or give any help.