The former Yeovil MP and Liberal Democrat Leader Lord Paddy Ashdown is being treated for bladder cancer.
He told Somerset Live he had been diagnosed three weeks ago and is being treated at Yeovil Hospital.
A Liberal Democrat spokesperson said: "Paddy informed colleagues of his illness two weeks ago.
"We wish him a speedy recovery and know that he will fight this with the vigour of a person 40 years younger.
"We all send our love to him, Jane and the family."
Lord Ashdown began his career in the military as a Royal Marine, before going on to represent the people of Yeovil from 1983 to 2001.
Ashdown led the Liberal Democrats into two general elections, in 1992 and 1997.
A number of senior party figures and Bath party members have tweeted support for their friend and colleague.