Ocado shares have jumped after reports that the company could tie up with Marks and Spencer when the High Street giant launches its online food service.
At the weekend, the Daily Telegraph said Ocado and M&S planned to start talks in the coming weeks.
The benchmark FTSE 100 index rose 38.09 points, or 0.5%, to 7,242.03, helped by energy giant BP.
Shares in BP rose 1.7% after it reported improved first-quarter profits from a year ago, helped by higher oil prices.
Underlying replacement cost profit - the company's preferred measure - was $1.5bn. That was better than analysts had forecast and compared with a $532m profit a year ago.
Pharmaceuticals group Shire saw its shares climb 2.4% after it reported a 14% increase in first-quarter earnings, beating expectations.
Back in the FTSE 250, shares in Aberdeen Asset Management rose 3.7% after it reported a 10% rise in half-year revenues.
The fund manager also said that its planned merger with Standard Life was "on track" and should be completed later this year.
But shares in online takeaway food ordering service JustEat fell 2.7% despite the company reporting a 46% rise in sales to £118.9m for the first three months of the year.
On the currency markets, the pound was given a boost by a stronger-than-expected survey of the UK's manufacturing sector.