Blue chip shares were on the front foot, boosted by a weaker pound after a poll showed the Conservative lead over Labour narrowing with less than two weeks to the general election.
A YouGov poll for The Times, conducted in the wake of the Manchester terror attack, puts the Conservatives on 43%, a drop of one point, while Labour is up three on 38%. A lead of just five points.
The FTSE 100 Index lifted 16.6 points to 7534.3, with the survey adding that if such numbers were replicated in every constituency on June 8 the Tories would actually lose seats and end up with a slimmer majority than the 17 it currently enjoys. The FTSE 250 Index rose 48.8 points, to 20016.4, passing 20000 for the first time.
The poll knocked confidence in the pound putting it on course to be the worst-performing major currency this week - falling 1.2% so far against the dollar and euro.
Conversely, this buoyed international firms in the Footsie as a weaker pound helps exporters. Top flight shares hit a fresh mid-session high of 7549.9, beating the previous record set just last week.
IG chief market analyst Chris Beauchamp said: "A weaker pound is doing wonders for the UK market this morning, helping both the FTSE 100 and FTSE 250 to hold in positive territory."
In the second tier the owner of Frankie & Benny's said sales slipped at the start of its year, despite good weather and strong cinema releases, as the firm bids to revive its fortunes.
The Restaurant Group, which owns 491 UK outlets including Garfunkel's and Chiquito, said sales in stores open for more than a year fell 1.8% in the 20 weeks to 21 May. Total group sales were down by 1.5%.
But shares jumped as the fall was much less that investors feared, suggesting the new management's turnaround is beginning to take hold. The Restaurant Group was 9% higher, or 28.1p to 345.5p.
The biggest afternoon risers in the FTSE 100 Index were Informa (+36p to 686.5p), Rolls-Royce Holdings (+16.5p to 868p), Randgold Resources (+120p to 7215p), Johnson Matthey (+52p to 3147p) and Hikma Pharmaceuticals (+26p to 1691p).
The biggest afternoon fallers in the FTSE 100 Index were Royal Bank of Scotland (-4.8p to 261.2p), Lloyds Banking Group (-1.1p to 72p), United Utilities (-14p to 1040p), Standard Life (-4.8p to 384p) and DCC (-85p to 7325p).
The biggest afternoon risers in the FTSE 250 Index were Restaurant Group (+28.1p to 345.5p), Spirax-Sarco Engineering (+460p to 5770p), Countryside Properties (+16p to 319p), GVC Holdings (+35.5p to 817.5p) and Wizz Air Holdings (+95p to 2299p).
The biggest afternoon fallers in the FTSE 250 Index were Petrofac (-38p to 392.8p), Britvic (-25.5p to 697.5p), Tate & Lyle (-21p to 728p), Evraz (-5.4p to 193.6p) and ZPG (-10.1p to 364.2p).