London's markets continued their strong week with the FTSE-250 hitting a record high as further vaccine fears pressed on the pound.
Currency traders were shaken after the UK's medical advisory body, the MHRA, said under-30s will be offered an alternative to the Oxford-AstraZeneca vaccine because of links with rare blood clots.
The drop in the currency helped lift UK multinational firms higher, with the FTSE-100 now just short of a new 12-month high.
The FTSE-100 closed 61.77 points, or 0.91%, higher at 6,885.32 on Wednesday.
Connor Campbell, financial analyst at Spreadex, said: "Much like on Tuesday, pronounced losses for the pound helped the FTSE top the table of the session's high fliers.
"It appears that while the UK blue-chip index, and its mid-cap sibling, enjoy the optimism surrounding the country's post-Covid comeback, sterling has been saddled with concerns over the vaccine programme.
"Compounding fears that arose from Sage's warning yesterday that the UK's vaccine rollout could severely slow down in the coming weeks was the latest Oxford vaccine update from the MHRA."
Sterling plunged against the dollar which has itself sunk quickly, sliding to a two-week low as the Federal Reserve is expected to continue to hold off tightening policy.
The pound fell by 0.51% against the greenback to $1.375 and was down 0.6% against the single currency at €1.157.
Elsewhere in Europe, the markets were far more subdued, as the German Dax decreased by 0.24% and the French CAC moved 0.01% lower.
Across the Atlantic, the US markets opened slightly higher, after a modestly negative session on Tuesday, with the shares of cruise companies getting a lift from positive booking numbers from Carnival.
In company news, Deliveroo made gains on its first full day of trading in spite of a rider strike over working conditions.
The takeaway delivery firm is nevertheless more than one-quarter down against its flotation price after it was shunned by many major investors last week.
Shares in the company closed 6p higher at 286p.
Royal Dutch Shell saw its shares edge upwards after the oil giant said it expects its adjusted earnings to be positive on the back of recent energy price rises.
However, it also told investors it expects the recent Texas snowstorm will have an adverse impact of up to $200 million on its adjusted earnings in the first three months of the financial year. It closed 14.8p higher at 1,440.4p
Paddy Power owner Flutter saw its shares slump after Rupert Murdoch's Fox media group filed an arbitration claim against it regarding the value of its stake in sports betting platform FanDuel. Flutter finished 210p lower at 15,535p.
The price of oil slipped back after Opec+ members decided to modestly increase the level of production in May and June.
The price of Brent crude oil decreased by 0.41% to $62.48.
The biggest risers on the FTSE-100 were Just Eat Takeaway, up 345p at 7,165p, DS Smith, up 12.1p at 424.4p, Informa, up 16p at 586.6p, and Pershing Square, up 70p at 2,720p.
The biggest fallers of the day were Flutter, down 210p at 15,535p, LSE, down 92p at 7,278p, Renishaw, down 80p at 6,445p, and AstraZeneca, down 84p at 7,099p.
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