The Right Honourable Robert Banks Jenkinson , 2nd Earl of Liverpool ( 7 June 1770 - 4 December 1828 ) was a British politician and the longest serving Prime Minister of the United Kingdom since the Union with Ireland in 1801 . During his time as Prime Minister from 1812 to 1827 , Liverpool became known for repressive measures introduced to maintain order , but also for steering the country through the period of radicalism and unrest that followed the Napoleonic Wars .