The FTSE 100 fell 0.1%, with international companies including AstraZeneca and Unilever weighing the most, while the more domestically-focussed FTSE 250 inched 0.1% higher.
Diageo, the world's largest spirits company and another stock sensitive to moves in sterling, lost 2%. Reuters reported on Thursday that unions were demanding a 5% pay rise for workers due to go on strike in Scotland later this month.
Among midcaps, Woodford Patient Capital Trust, money manager Neil Woodford's listed fund, fell 7% after the trust's administrator cut the valuation of one of its holdings.