Mortgage with a weak debt record

My son had a poor debt record in a previous relationship, but all debts were settled when they split up. He has recently married and has inherited a sum of money, adequate for a 50% deposit on a new home loan.
Because of his poor credit ratings, what sort of mortgage interest rates could he expect to pay to any lender. We would like this information up front before we start looking for suitable family homes.

Thanks Baz