Who is Mr Mortimer?

The persona of Mr Mortimer emerges in the afternoons. But who is he in real life? What is his connection with the death of Mrs Hughes? Can Dave Willetts, insurance investigator, unravel the connections between O'Donnel, his waste recycling empire and the land owned by Mrs Hughes. When solicitors' negligence is uncovered can Dave Willetts avoid a large payout for his company?