The plan came to fruition in August 2014, when Carswell shocked Westminster by announcing his defection.
Ukip pulled out all the stops to get him elected in the subsequent by-election, with Farage even forgoing campaigning in another by-election taking place on the same day.
As it was, Ukip won the Clacton seat comfortably, but lost the Heywood and Middleton by-election by fewer than 600 votes.
Almost as soon as he was elected, Carswell appeared to be at odds with his leader and refused to back Farage’s claim that migrants with HIV should be banned from the UK.
The pair continued to fall out, culminating with Carswell backing a rival Brexit campaign – Vote Leave – to the one which had Farage’s support, Leave.EU.
Article source: http://www.huffingtonpost.co.uk/2016/10/02/douglas-carswell-infiltrated-ukip-to-neutralise-nigel-farage_n_12295018.html?utm_hp_ref=uk-politics&ir=UK+Politics