Conservative MP Stephen Phillips has quit over "irreconcilable policy differences" with the government.
The MP, who has held the Lincolnshire seat of Sleaford and North Hykeham since 2010, backed leaving the EU but has accused ministers of ignoring Parliament since the Brexit vote.
He said he was "unable properly to represent the people who elected me".
It comes as Theresa May said she was confident she would win a legal battle over her approach to Brexit talks.
Friday, 4 November 2016
BBC News: Tory MP Stephen Phillips quits over 'irreconcilable differences'