Complex sentence: Osborne cannot have expected to hold office for much longer: his prestige had sunk so low that his office was offered to Sir John Meade, who had previously been regarded as completely ineligible because his wife was a Roman Catholic.
Split into simpler sentences: Osborne cannot have expected to hold office for much longer. His prestige had sunk so low that his office was offered to Sir John Meade, who had previously been regarded as completely ineligible because his wife was a Roman Catholic.