The British pound is highly vulnerable and on course to trend towards parity with the U.S. dollar and the euro, Beat Wittmann, partner at Porta Advisors, warned on Thursday.

Chaotic domestic politics are the key reason for Wittmann's pessimistic outlook, with the financial advisor accusing Prime Minister Theresa May of remaining "incompetent, ignorant and selfish".

"U.K. domestic politics will, for the foreseeable future, remain highly unpredictable and ineffective, creating a steady erosion of consumer and investment confidence and ongoing uncertainty for businesses including the City," predicted Wittmann, speaking on CNBC's Squawk Box and in further thoughts sent via email on Thursday.

Anticipating a very difficult period ahead for the U.K., the industry veteran says nothing particularly constructive is likely to happen in Brexit negotiations until the prime minister is replaced.

"May is a spent force with (foreign secretary) Boris Johnson or (Brexit minister) David Davies likely to replace her within next few months. This will be perceived very, very negatively by the European Union (EU) and global investors and will be followed by new elections within the next 12 months," posited Wittmann.

"Labour party leader Jeremy Corbyn could potentially win such an election which would make matters worse still," he continued.