ESA Letter

I have secondary progressive MS and was placed in the support group, with your help in 2013.
I received a letter today from the DWP, asking me to fill in a form as part of their research.It says it is an anonymous questionaire but it is asking questions like,
1) would you be willing to go back to work?
2) do you feel able to go back to work?
3) Is your health condition worse or better now?
It then asks for a detailed response from me about any work I could do,about the hours I could work and when I could return to work.
It does say this is voluntary, I am worried that if I don't reply, there will be a problem. likewise I am unable to work, do I just write that?
I would be grateful for any advice.

I would ignore this letter.

File it away though, don't destroy it.

If you ever hear more from them come back and tell us.