US firm Reynolds American's takeover of rival Lorillard was cleared by regulators on Tuesday, on condition that the firms sells the Winston, Kool, Salem and Maverick brands.
Imperial Tobacco is set to buy the brands, and its shares rose 2.4%.
The FTSE 100 index was up 32.56 points at 6,981.55.
Shares in British Airways owner IAG rose 1.6% as the airline group closed in on a takeover of Irish carrier Aer Lingus.
On Tuesday, the Irish government agreed to sell its 25% stake in Aer Lingus to IAG, removing a major hurdle to the deal.
In the FTSE 250, shares in De La Rue dived 8.8% after the banknote printer reported a drop in profits and slashed its dividend.
Underlying operating profit for the year to 28 March fell to £69.5m from £89.3m a year earlier, and the banknote printer cut its dividend by 40%.
On the currency markets, the pound rose 0.19% against the dollar to $1.5414, but fell 0.09% against the euro to €1.4130.
(Open): Shares in Imperial Tobacco led the FTSE 100 higher after the firm moved closer to the purchase of four cigarette brands.