The FTSE 100 index has closed above 6,000 points for the first time since June 2008.
The index of blue chip shares broke through the symbolic mark to finish up 12.85 points, or 0.2%, at 6008.92.
A late rally in retail stocks helped the index as investors bet on a late surge in consumers' Christmas spending.
However one analyst forecast that there would be a correction in share prices after an overly-strong rise in December.
Giles Watts, head of equities at City Index, added that the lack of trading volume meant that Friday's rally was built on "hot air".
The index has risen 8% so far this December, its strongest for the month since 1987.
With its move above 6,000 points, some observers are claiming London has regained a poise not seen since before the collapse of Lehman Brothers in September 2008, which caused turmoil on world markets.
The FTSE 100 is up 10.8% on the year, with several bullish market analysts predicting that the index may end 2011 between 6,600 and 6,900.
On Friday, Marks & Spencer, Next, B&Q parent Kingfisher, and supermarket giant Tesco were all in strong demand.
And troubled sports retailer JJB Sports added 22.6% after saying it hoped to raise more than £31.5m in a share sale.
Friday's FTSE close is the fourth straight weekly advance.
"The prolonged Santa rally has left the market looking strong ahead of the holidays and there is still the potential for further gains before the end of the year," said David Jones, equity strategist at IG Index.
France's Cac 40 index slipped 0.3% to 3,900.4, but there was no trading in Germany where on Thursday the Dax index had slipped 0.2% to 7,057.7.