The blue-chip FTSE 100 gained 2.9% by 0812 GMT, but was still underperforming its European peers, weighed down by news that Prime Minister Boris Johnson was in hospital due to persistent symptoms, 10 days after testing positive for the virus.
The domestically focused midcaps gained 3.4%.
Stock markets globally were on steadier grounds after last week's modest selloff as the rate of new infections and deaths slowed in Italy and Spain, while hard-hit New York reported on Sunday that deaths had fallen slightly from the day before.
Aero-engine maker Rolls-Royce rose 10.6% after revealing it had secured an additional 1.5 billion pounds ($1.8 billion) revolving credit facility, but said it was scrapping its targets and final dividend.Legal & General Group surged 13.7%, recovering sharply from last week's losses after the insurer said it planned to pay its 2019 dividend even after a European Union regulator said insurers should temporarily halt payouts. Healthcare company Novacyt rose 8.3% after its COVID-19 diagnostic test won French approval, making it available for immediate distribution in France.