Blue chip shares lifted as the pound slipped following continuing Brexit concern and a worrying economic report.
Tax is set to rise as a share of the UK's income to its highest level since 1986, according to the influential Institute for Fiscal Studies. It said higher income from taxes and relatively low growth will combine to create this effect.
The FTSE 100 Index rose 45.7 points to 7218 in afternoon trading, as sterling hit a two-week low of $1.2350 against the dollar as a result of ongoing uncertainty surrounding the Brexit process. The FTSE 250 Index lifted 197.6 points to 18575.
Overnight, a series of Article 50 Bill amendments failed, spooking investors' mood as the process of taking Britain out of the European Union remains clouded in uncertainty.
Top flight shares appeal to investors when the pound falls because most of the sales of firms in the index are earned aboard, boosting revenues when translated back into sterling.
Spreadex financial analyst Connor Campbell said: "There wasn't a lot of good news for sterling to cling on to."
In London, BP posted its second annual loss in a row, as weak oil prices continue to hit the oil industry.
The oil giant said its full-year replacement cost loss narrowed to $999m last year as it faced "challenging" oil prices, from a loss of $5.2bn the year before.
BP was the biggest faller in the top flight with shares down more than 2%, or 11.6p to 465p.
The biggest afternoon risers in the FTSE 100 Index were DCC (+360p to 6735p), Fresnillo (+53p to 1541p), Pearson (+18.5p to 662.5p), Rolls-Royce Holdings (+19p to 699.5p) and Dixons Carphone (+8.2p to 313.5p).
The biggest afternoon fallers in the FTSE 100 Index were BP (-11.6p to 465p), CRH (-40p to 2774p), Standard Chartered (-7.2p to 796.4p), EasyJet (-7p to 925.5p) and Ashtead Group (-4p to 1637p).
The biggest afternoon risers in the FTSE 250 Index were Berendsen (+60.5p to 906.5p), FirstGroup (+6.3p to 110.3p), Hochschild Mining (+14.4p to 262.7p), Kaz Minerals (+29p to 541p) and Ferrexpo (+7.8p to 161p).
The biggest afternoon fallers in the FTSE 250 Index were Euromoney (-32p to 1065p), Tullow Oil (-6.6p to 299p), Millennium & Copthorne Hotels (-8.5p to 416.5p), Evraz (-3p to231.5p) and NMC Health (-20p to1716p).