At 0914 GMT, the pan-European STOXX 600 index was down 0.2 percent, with heavy losses notably on London's FTSE , which slipped 0.6 percent.
Weighing on the British blue-chip index was holiday firm TUI , the shares of which fell close to 10 percent after it blamed a summer heatwave for keeping Europeans at home instead of traveling.
"There's a chance the FTSE's losses would have been even greater on Thursday if the pound didn't get off to another awful start", said Spreadex's Connor Campbell.
The market analyst added: "the fears of a 'no deal' Brexit have really gathered steam in the last few sessions".
A weak pound typically gives an accounting boost to blue-chip UK companies, which sell a large proportion of their products or services in foreign currencies.
The ongoing earnings season prompted other steep moves among companies publishing quarterly results.
German sportswear firm Adidas posted the best performance after it reported a better-than-expected second quarter and saw its shares jump 8 percent, on track for their best day since the group raised its guidance in March.
Lifting the consumer discretionary sector, one of the only subsets of the stock market trading in the black, was cinema operator Cineworld, which posted a 10.8 percent rise in half-year revenue, lifted by blockbusters such as "Avengers: Infinity War" and "Black Panther".
In the banking sector, Austria's Raiffeisen Bank surpassed expectations in the second quarter, but its shares fell over 5 percent as new US sanctions against Russia put pressure on companies with exposure to the country.
Raiffeisen said it was too early at this stage to say who would be affected by the sanctions.
CMC Markets analyst Michael Hewson said in early trading that "concerns about new US sanctions on Russia", alongside trade war fears, "may well also limit the upside for European markets today".
Belgian bank KBC fared better with its results, with its shares up 1.3 percent after it announced the sale of a 1.9 billion euro loan portfolio to Goldman Sachs.
In a rather unloved sector at the moment, Deutsche Telekom rose 0.2 percent after a choppy start. The German group raised its profit outlook for the second time this year as it reported second-quarter results.