Can I work while in the ESA Support Group?

Hello, 
I called the DWP but the person I spoke to was highly rude and questioning my reason for wanting to work. I'm age 39, recently taken partial medical retirement from my teaching job due to cancer. 
I receive £113 each week in the support group BUT I also receive a small private pension (which I have already declared and given proof). The pension is £66.75 per week. I read somewhere that I could potentially earn up to £140 per week whilst in the support group, but does this mean I would have to take into account my pension? E.g. £140 - £66.75 = £73.25 earning potential per week? 
Thank you in advance for anyone who may be able to give insight into this. As previously mentioned, I've found the DWP, in general, to be judgemental and difficult to deal with.

Ross