Assuming you are in the UK, it is important to realise that solicitors are required by law to cover their backsides against various possible accusations by government authorities. These centre on asking for all sorts of "proofs". The solicitor will take the attitude that you are guilty of something until he/she is satisfied he/she has likely graduated from being seen as guilty until proven innocent by the authorities. Neither you or he/she can know what you might be asked for because it depends on how frightened he/she is and what his/her imagination stretches to. The aim of the solicitor is to make your life difficult to at least the same extent as the authorities make his/her life difficult.