the prime minister travelled from london to penzance on the sleeper train .
he looked stressed and exhausted as he got off the train this morning .
cameron was sporting jeans with smart black shoes and a navy jacket .
tories are keen to drive the lib dems out of the south-west at the election .
labour are still ahead in the polls nationally , with 34 % set to back the party .
tories are 1 % behind , on 33 % , with the lib dems on 7 % and ukip on 14 % .