‘Well, they say to themselves: he [Jeremy Corbyn) may be a mutton-headed old mugwump, but he is probably harmless.”

Boris Johnson, The Sun

"Mugwump: (North American) A person who remains aloof, or independent, especially from party politics."

Online Oxford English Dictionary

"The word was sometimes jestingly applied in early America to someone who was the "head guy." The first political mugwumps were Republicans in the presidential race of 1884 who chose to support Democratic candidate Grover Cleveland rather than their own party's nominee. Their independence prompted one 1930s humorist to define a mugwump as "a bird who sits with its mug on one side of the fence and its wump on the other."

Merriam-Webster online dictionary

“On stools covered in white satin sit naked mugwumps sucking translucent, coloured syrup through alabaster straws. Mugwumps have no liver and nourish themselves exclusively on sweets. Thin, purple-blue lips cover a razor-sharp beak of black bone with which they frequently tear each other to shreds in fights over clients.”

William Burroughs, The Naked Lunch

"'But my dear old muddleheaded mugwump,' said Mr Wonka, turning to Mrs Bucket. 'What does it matter that the old girl has become a trifle too old?'"

Charlie and the Great Glass Elevator, Roald Dahl