The FTSE 100 hit a record at 6,958.89 points nearing the end of the day's trade and after the eurozone had backed a four-month extension to Greece's financial lifeline.
It went on to reach a record close at 6,949.63 points after rising 0.54 per cent compared with today's finish.
"After 15 years of market ups and downs since the peak of the dotcom boom, the FTSE 100 did it, a new all-time high," said Jasper Lawler, analyst at traders CMC Markets UK.
Indices on Wall Street have already struck record-highs this year.
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A recovery to commodity prices has meanwhile boosted share prices in heavyweight mining companies traded on the FTSE index of 100 companies.
The index includes companies ranging from energy giants BP and Shell to banks HSBC and Barclays as well as miner Rio Tinto, mobile phone group Vodafone, British Airways-parent IAG and pharmaceutical firm GlaxoSmithKline.
"The current level of the FTSE is underpinned by company profits to a much greater extent than it was in 1999," said Laith Khalaf, senior analyst at Hargreaves Lansdown stockbrokers.
"However, risks still lurk in the background. The agreement reached in Europe (over Greece) is a sticking plaster to allow further negotiations to take place and may well flare up again. The UK election (in May) will also cause some thrills and spills, as markets weigh up the implications of potential outcomes.