Letter from DWP - I may be able to get more ESA

Hello all, out of the blue I have received a letter from DWP telling me I may be able to get more ESA. I had been on incapacity benefit since 2003 & when ESA was introduced between Feb 2012 - Feb 2013 DWP paid me contribution based ESA. They are now saying I may be eligible for income related ESA during that period & could receive extra payments called premiums. I didn't have savings anywhere near the limit, nor did I have a partner bringing money in, so it seems I do qualify for the extra money.

Accompanying their letter was a 44 page form which I have to complete relating to my circumstances & finances during that period.

My question to you is, has anybody else had a letter like this & does anybody know roughly what amount I could receive. If its only a matter of a few pounds then its not worth me completing the form, but they haven't given me any idea of the amount I could be eligible for.

Hoping you can help. Many thanks.

Thank you Gordon.