The Footsie 100 Index is up 44.5 at 4213.9 at lunchtime.
Hopes of a strong start on Wall Street helped push the index past the 4200 barrier.
City traders were looking for a strong start in the US later this afternoon after a weak half-day session on Friday.
Then markets were subdued by the Thanksgiving festivities but most were expecting a return to form for Wall Street today.
In London mmO2 led the charge, up 7% or 3.5p to 54.5p, rival Vodafone increased 2.5p to 124.5p, Cable & Wireless lifted 7p to 89p and BT gained 3.25p to 213.25p.
There was also a surge of confidence for financial stocks, with HBOS up 24p to 720.5p, Lloyds TSB gaining 24.5p to 567p, Barclays rising 14.5p to 479,5p and Royal Bank of Scotland 38p stronger at 1686p.
Even troubled mortgage bank Abbey National was stronger, nudging forward 4.5p to 652p.
Insurers on the move included Legal & General, up 4.25p at 119.25p, Aviva, ahead 23.5p to 572p and Royal & Sun Alliance, 7.75p stronger at 155p.
In a quiet session for corporate news, focus fell on developments over the weekend, including reports that transport group Stagecoach will sell its US bus operation later this week.
The group is scheduled to post interim figures on Wednesday but ahead of that, shares rose 10% or 1.75p to 19.75p.