In its listing prospectus, published on Friday ahead of a planned Sept. 12 trading start, Uniper said that its large exposure to Britain, where it owns 7 gigawatt of mostly gas and coal-based generation capacity, carried substantial risks.

"The withdrawal of the United Kingdom from the EU could affect the Uniper Group in a number of different ways and could have a material adverse effect on the Uniper Group's United Kingdom and overall business, prospects, financial condition and results of operation," it said.

(Reporting by Christoph Steitz; Editing by Maria Sheahan)