Hello sam,
it is very hard for us to give good advice in a situation such as yours without knowing the complete picture.
The DWP will help you to fill the form in by reading out the questions and writing in your answers.
What they will not do is carefully consider your case and put it in the best way possible. Do you have a friend or a relative who could help you with this?
If you cannot face doing the form alone, and you don't have someone who is able to help you, then yes, ask the DWP to help you.
And yes, you would need to send in your evidence separately.
Hope this helps
Catherine
Nothing on this board constitutes legal advice - always consult a professional about specific problems 
