You are out of time I think.
I have just tried to claim compo for tripping in a supermarket, and thought I had it all in my favour - witnesses accident book, two months off work and to cap that an MRI scan that confirmed I had suffered a serious knoock to the knee.
Unfortunately, there are too many get out clauses for the other party, and the same would apply to a council (ie, did you trip in a road? - they can claim it was checked within a certain time period and get out of it that way) but getting back to the 3 years, I was trying a no win no fee job, and he said he couldn't touch it but if I wanted to pay and proceed, make sure I did it within 3 years of the accident.