The FTSE 100 Index has ended a previously lacklustre session 53.2 points ahead at 5127.0.
This was due to a tentatively upbeat start on Wall Street and strong gains by BT, which surged 5% or 11½p to 238½p.
A number of other telecom stocks were gaining in BT's wake, with mmO2 moving up 3½p at 74p and Vodafone adding 7¾p at 144¼p.
Elsewhere, Smith & Nephew was ahead after cheering the City with its full-year results. Shares lifted 13p at 413p.
In a busy day for corporate updates, news of another improved bid from US giant Carnival added buoyancy to cruise line operator P&O Princess' value. The UK group said its board would meet to discuss the £3.8 billion offer and shares gained 6½p at 409½p.
Heavyweight financial stocks were also ahead, regaining recent losses following the revelation yesterday of rogue trading at Allied Irish Banks' US subsidiary.
Those adding their weight to the wider market included Lloyds TSB, up 25½p at 752p, Abbey National, 28p stronger at £10.60, Royal & Sun Alliance, 18p higher at 320p and Prudential, ahead 24½p at 738p.
Key oil stocks were also down after Shell disappointed the market with fourth quarter figures below expectations.
Hit by the low price of crude oil, Shell lost 3p at 481p while BP was down 4p at 545p and Enterprise Oil was off 9p at 610p.
Logica, a specialist in text messaging, also fell after FTSE 250 rival CMG unveiled a £100 million deal with Hutchison 3G. The deal, to handle all messaging traffic sent on next generation phones sold by Hutchison, sent CMG soaring 17¼p to 249p while Logica slumped 13p to 510p.