After ending last week 1.7 per cent lower than it started, the index was 1.4 lower in mid-afternoon trading, at 6,685 points
The fall was led by Primark owner Associated British Foods (ABF), which fell 10.2 per cent to 2,883.5p after it warned post-Brexit currency volatility could dent profit margins next year.
Miners were also casualties, with BHP Billiton falling 3.7 per cent to 979.35p and Anglo American dropping 3.9 per cent to 813.9p.
European shares were hit last week by a warning from European Central Bank chief Mario Draghi, who said the region's economic recovery is likely to be dampened by Brexit.
"The risks to the euro area growth outlook remain tilted to the downside and relate mainly to the external environment," he said - although the ECB did raise its forecast for growth to 1.7 per cent, from 1.6 per cent.
But this morning analysts suggested it could be more of the same when the Federal Open Market Committee (FOMC) meets next week.
"Investors have got a case of the pre-Fed jitters, exacerbated by the lack of distractions this Monday, meaning noted FOMC dove Lael Brainard’s speech later this afternoon has gained more market-importance than it arguably deserves," said Connor Campbell, finanical analyst at SpreadEx.
"Even the slightest sign of hawkishness from Brainard is going to be a big deal, and could see this early slump extend into the rest of the week."