The FTSE 100 index lost 0.7 percent on its worst day in a month, but the midcaps gained 0.4 percent with gold miner Centamin leading gains after a strong quarterly update.
The blue chips, which had touched a near seven-month high in the last session, lagged European markets where strong earnings from the likes of SAP and Credit Suisse kept a lid on losses.
Bellwethers Shell and BP dropped from multi-month highs as crude prices retreated after having jumped to their 2019 highs this week as the United States pushed to tighten sanctions against Iran.
Shell, the most valued FTSE 100 component in terms of market cap, recorded its worst day in over a month, while BP suffered its biggest one-day drop since late January.
Further weighing on the index were mining companies which fell nearly 2 percent as the price of industrial metals dropped in Shanghai on growing concern that China, the world's biggest metals consumer, will ease up on its economic stimulus efforts.
Anglo American, with a 4 percent decline, was among the biggest blue-chip losers, after JP Morgan cut its rating on the stock.
Sainsbury's gave up 1.6 percent. Britain's competition regulator is expected to publish its final report on the supermarket group's planned takeover of Walmart-owned rival Asda on Thursday.
A bright spot, though, was Associated British Foods, which added 2 percent after its first-half results showed profit at its Primark chain jumped thanks to an expansion drive.
"Despite having no online presence, Primark has shown that there is money to be made in the retail sector if your know your market and maintain control of your costs and inventory," said CMC Markets analyst Michael Hewson.
Online fashion retailer Boohoo jumped 10.3 percent to levels not seen in over six months as its strong profit numbers bucked the trend in a tough market for clothing retailers.
Boosting the midcap bourse was precious metals miner Centamin that leapt 13 percent, its biggest intra-day gain in nearly three years, as its first-quarter production beat the company's forecast.
Saga rose 6 percent after JP Morgan said the motor insurer had reset expectations with recent results and upgraded its rating on the stock.
A standout gainer on the day was small-cap KCOM that increased its value by one-third, ending the day at 96.9 pence. That almost matched a 97 pence a share takeover bid from Britain's pension fund Universities Superannuation Scheme.
KCOM, which according to a media report in February was also eyed by Virgin Media, jumped 34 percent on its best day in nearly two decades.
(Reporting by Muvija M and Shashwat Awasthi in Bengaluru; Editing by Larry King and Mark Potter)
By Muvija M