A focus on major deals in the pharmaceuticals sector added billions of pounds in value to the UK's biggest players GlaxoSmithKline and AstraZeneca.
The flurry of activity helped the FTSE 100 Index surge 1% or 66.8 points to 6692 as investors overcame their fears about the prospect of more sanctions against Russia in relation to the crisis in Ukraine.
AstraZeneca shares were 7% higher after weekend reports that larger US rival Pfizer had made a tentative approach that could possibly value it at more than £60 billion.
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Astra has reportedly resisted the advances, with no talks currently under way, but it is thought that Viagra maker Pfizer could come back with a fresh approach - a move that would mark the biggest-ever foreign takeover of a UK business.
Astra's shares were almost 10% higher at one point, adding £4.6 billion to its worth, though this later settled back to around 263.5p higher at 4045.75p.
The rise outstripped the gain posted by GlaxoSmithKline after a three-part deal was announced with Swiss-based firm Novartis that included a combination of the pair's consumer healthcare arms.
Glaxo was 87p higher at 1646p as it emerged that the UK company will use some of the £9.5 billion proceeds from the sale of its oncology portfolio to Novartis to return cash to shareholders. It will also acquire Novartis's global vaccines business, adding four products to its late-stage pipeline.
Today's share price rally reversed falls in recent weeks due to ongoing concerns over the strength of its pipeline of new drugs and corruption allegations in Iraq and China.
The round of deal-making in the drugs sector also benefited shares in Shire, which rose 4% or 124p to 3049p, while Hikma Pharmaceuticals was 68p higher at 1564p in the FTSE 250 Index.
Elsewhere, shares in drinks giant Diageo recovered from the sell-off seen on Thursday in the wake of a disappointing trading update to stand 37p higher at 1866p, while Royal Mail was 12.75p stronger at 521.75p.
Retailers were also doing well after decent weather over the Easter weekend fuelled hopes for improved trading.
Marks & Spencer rose 6.7p to 441.2p and Sports Direct International pulled back from recent weakness to climb 26.5p to 825.5p. FTSE 250 Index rival JD Sports Fashion was 80.5p higher at 1815.5p.
In other corporate news, shares in defence products firm Qinetiq fell 2.35p to 219.25p after it announced the sale of its US services division for 215 million US dollars (£128 million).