In 1698, Duncombe was arrested and imprisoned in the Tower of London, and subsequently expelled from the House of Commons, for "contriving and advising the making of false Indorsements of several Bills, made forth at the Receipt of Exchequer, commonly called Exchequer-Bills", in other words a tax fraud. He was expelled from the House of Commons on 1 February 1698.
Duncombe faced repercussions in 1698 when he was detained at the Tower of London and subsequently barred from participating in House of Commons activities, due to his involvement in fabricating false endorsements for Exchequer-Bills, a form of tax evasion. His expulsion from the House of Commons occurred on February 1, 1698.