The FTSE 100 ended up 21.33 points, or 0.3 percent, at 6,873.08 points.
FOREX.com technical analyst Fawad Razaqzada reckoned there was scope for the index to hit 6,950, the record peak set 14-1/2 years ago, and then the 7,000 level. "But we could go far beyond those levels over the medium term," he said.
Housebuilding shares, which have surged over the last year on the back of a booming UK property market, outperformed.
Persimmon and Barratt Developments both rose 3.2 percent, the top FTSE 100 risers, after smaller rival Taylor Wimpey said sales rates were at the upper end of its expectations, sending its shares up 7.6 percent.
Some analysts said the sector's gains, which have seen the Thomson Reuters UK Homebuilding index rise almost 70 percent since the start of 2013, might fade on prospects of an interest rate rise in Britain next year.
"I'd be tempted to sell into any rallies on the housebuilder shares," said Beaufort Securities sales trader Basil Petrides.
Petrides also expected the FTSE 100 to hit a record of 7,000 points at some time later this year but said the index had to first sustain a break past its May 2013 high of 6,875.62 points.
EasyJet limited the index's gains as investors took profits on the low-cost airline after a powerful rally.
EasyJet has jumped around 50 percent over the last 12 months, but it fell 4.2 percent after posting a first-half loss that beat forecasts. Its drop made one of the biggest dents on the UK benchmark in terms of points.
"EasyJet's one of my favourite stocks, but they've had a fantastic run," said Joe Rundle, head of trading at ETX Capital, "Just a bit of profit-taking; looks like it should bounce around 16 quid." The shares are trading at 1,658 pence.
Strength in AstraZeneca helped to steady the index. U.S. rival Pfizer suggested it could increase its offer of 50 pounds ($84.4) a share for the British drugmaker if AstraZeneca would only engage in talks.
AstraZeneca, which has surged more than 20 percent since Pfizer indicated in April it wanted to buy the firm, rose 0.7 percent to 4,642 pence.
($1 = 0.5927 British Pounds)