The blue-chip FTSE 100 was down 1.4% by 0709 GMT, with BP and Royal Dutch Shell tracking a slide in oil prices.
Mining and financial stocks were also among the biggest decliners. No single FTSE 100 stock posted gains in early trading.
The mid-cap FTSE 250 tumbled 1.1% as Prime Minister Boris Johnson lifted most restrictions in England in what some have dubbed “Freedom Day” despite a new wave of COVID-19 cases.
Travel-related stocks sank for the fifth time in six days as the surge in infections raised the spectre of new travel curbs.
British Airways-owner IAG and InterContinental Hotels fell more than 2.5% to the bottom of the FTSE 100.
(Reporting by Sagarika Jaisinghani in Bengaluru; Editing by Arun Koyyur)