I make no comment on the Iraq matter, except to say that Western armed forces are signatory to the Geneva convention and where it may appear to have been broken there should be an enquiry, and that if a person has acted illegally, as alleged for the Leigh Day's 'junior employee' over alleged destruction of evidence, they should face an appropriate enquiry. So far all enquiries have found that the 'destruction' of the document had no effect on the matters in hand. The use of this matter for political gain by Cameron is regrettable and not worthy - but that is no surprise. Leigh Day have responded to the 'allegations' here
https://www.leighday.co.uk/News/News-2016/January-2016/Statement-in-relation-to-referral-to-Solicitors-Di if anyone chooses to read what they have said.
For Leigh Day as an entity I do have experience. They successfully challenged a medical appliance company called de Puy in a 'group action' over the mis-manufacture of replacement hip joints (which has resulted in Mrs B having no less than 5 replacement operations on the same hip since 1997, leaving her unable to walk normally).
A (relatively inadequate) settlement was reached out of court, and Leigh Day are currently pursuing another action against de Puy for yet another alleged mis-manufacture of a hip joint leaving other recipients in difficulties.
Whatever one's feelings about so-called 'ambulance chasers' (and I do NOT place Leigh Day in this category), the legal system in the UK precludes the average person from bringing any sort of action against a company or body simply because of potential costs. Thus a company like Leigh Day are able to step in and take action for many. They are currently in the process of 'discussions' with VW on behalf of VW etc owners who have notified LD that they have 'problems' with the emissions scandal and are expecting the UK's largest ever legal group claim over this.
Leigh Day do not offer 'no win no fee' support for individual folk on a case by case basis as do the common 'ambulance chasers' but have a proud track record of helping groups affected by others' actions.