He was elected for the UK Independence Party (UKIP) and served as national spokesman on trade from 2010 to 2018.

In January 2007, Dartmouth announced he was leaving the Conservatives in favour of the UK Independence Party (UKIP), citing concerns about the policies of David Cameron, then Leader of HM Opposition.

[8] Dartmouth condemned Batten for leading the party towards the far right and denounced his approval of and support for extreme right-wing groups and "outlandish individuals".

[9] Dartmouth said he would not be joining another political party and would serve the rest of his term in the European Parliament as an Independent, continuing to represent the South West of England and Gibraltar.

Dartmouth has a son, Gerald Glen Kavanagh-Legge (born 2005), from his previous relationship with the television producer Claire Kavanagh.