Tax return for housing compensation query

I need an answer to the following question
We have a claim with housing association being managed by a solicitor
they have negotiated compensation but in addition we are claiming for additional costs such as loss of earnings for approx 15 days - I am self employed
Why is my solicitor asking for my tax return - is it to show income or profit - but what is the reason ? as it was only for 15 days of the year that I couldn't work
Just interested really as to what they are trying to prove as i didn't work full time during the year anyway