In 2016, Trimble supported the Leave side in the UK referendum on EU membership. He said that if he had ever had any doubts about the issue, "his eight years on the EU Select Committees in the House of Lords – which scrutinise the EU's operations – had convinced him of the need to cut ties with Brussels". He cited a study which found that economic growth in the UK reduced after the decision to enter the Common Market, and reduced further when the UK went into the Single Market.