Duncombe continued to sit unopposed for Newport as the paying guest of its patron, Sir Leonard Worsley Holmes*. A lax attender, who is never known to have spoken in debate, when present he gave general support to the ministry of Lord Liverpool, from whom he extracted an assurance of promotion to the peerage in May 1820.
Duncombe spent his retirement at Duncombe Park tending an art collection which by 1831 included works by Poussin, Rubens and Leonardo da Vinci.
