The FTSE 100 closed down 28.9 points, or 0.5%, at 6,342.28.
Some weak trade figures from China put pressure on mining shares, with Glencore falling 2.6% and Anglo American down 1.8%.
Royal Mail shares fell 4.2% to 452.5p, after the government sold its final stake in the company.
The government said it had raised £591.1m from selling its final stake in Royal Mail at 455p a share.
Shares in brewer SABMiller jumped 9% to £39.48 after it agreed terms for a takeover by AB InBev.
SABMiller said it had agreed "in principle" an increased offer from its rival of £44 a share, bringing closer the prospect of a tie-up between the world's two largest brewing companies.
In the FTSE 250, shares in Bellway Homes rose 3.6% after the housebuilder reported a 44% increase in full-year pre-tax profits to £354.2m.
News that UK inflation turned negative again in September pushed the value of the pound down, as the prospect of an early rise in interest rates diminished.
CPI inflation fell to -0.1% last month from 0% in August. The CPI rate has been at or close to zero for most of this year, and was last in negative territory in April.
The pound was trading down more than a cent against the dollar at $1.5237, and was also down more than a cent against the euro at €1.3387.
Mining shares pulled the FTSE 100 lower, while Royal Mail shares dropped after the government sold its remaining stake in the company.