The FTSE had fallen earlier in the day, with investors concerned about the continued plunge of the rouble.
However the index strengthened on news of the Russian central bank's pledge to provide additional capital to the country's banks, if necessary.
Figures showing a rise in UK wage growth also cheered investors.
The price of Brent Crude oil, which has been falling for weeks, recovered by almost 4% late on Wednesday, reaching $62.32 a barrel.
Shares in oil firms Tullow Oil, BP, and BG Group all rose more than 3% as a result, with Royal Dutch Shell 'B' rising by 2.9%.
Meanwhile British Airways owner IAG fell by 4%.
Dixons Carphone rose 3% after it reported a 30% rise in underlying half-year profits.
The firm, which owns the PC World and Currys chains as well as Carphone Warehouse, said its UK and Ireland business had enjoyed a "barnstorming performance".
All eyes will be on the US Federal Reserve later when it announces the results of its latest meeting.
There is speculation that the US central bank will end its commitment to keep interest rates low for a "considerable period", suggesting a rate rise is moving closer.
On the currency markets, the pound fell 0.55% against the dollar to $1.5664 and rose 0.16% against the euro to â‚¬1.2609.

The 28-year-old, world champion in 2013 and twice a world cup series winner, is named pending a recovery from hand and wrist injuries sustained in February.
Senior academy rider Paddy Sharrock is set to make his elite level debut.
In the junior women's event, Beth Shriever heads to Rock Hill with five wins in the junior women's class of the UEC BMX European Cup so far this year.
Kyle Evans, who won the seventh round of the UEC BMX European Cup in Verona over the weekend, has also been selected.
Olympic podium coach Grant White is confident Phillips will overcome injury sufficiently and said: "Having worked with Liam for nine years and helped him develop into one of the world's best, I am confident in his ability to perform at this event despite setbacks and the team at British Cycling are doing all they can to aid his recovery."
Elite Men: Kyle Evans, Liam Phillips Paddy Sharrock
Junior Women: Beth Shriever, Blaine Ridge-Davis
Junior Men: Kye Whyte
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(Close): London's benchmark index, the FTSE 100, closed marginally higher on Wednesday, gaining 4.65 points in late trading to close at 6336.48.
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Liam Phillips has been included in the Great Britain squad for the UCI BMX World Championships in South Carolina.