Engineers and miners put brakes on blue-chip index Weir Group, which makes pumps and valves for industries including mining, slumped 125p to £19.54 too. But some suggested that the slide might be down to concerns over prospects for the shale industry. Production of unconventional oil and gas, where hydrocarbons are extracted from shale and sands, has grown rapidly in America. However, some in the City were pointing to comments at an industry event, where people were sceptical about the rate of growth. But, Oliver Wynne-James, an analyst at Panmure Gordon, said that he still expected the "unconventional oil and gas equipment market in North America to continue to grow by double digits this year despite the low seasonal price for natural gas." Among the second-liners, Ocado sped ahead. Since reassuring the market earlier this month with a 16pc rise in Christmas sales, the online grocer's shares have risen more than 18pc and it put on another 7.55 to 87.65p. It seemed that demand from long-only investors was behind the rise, with some in the Square Mile also reheating gossip that a supermarket chain could make a tilt at Ocado - a rumour which others in the City found highly dubious. Elsewhere on the high street, Marks & Spencer put on 7.7 to 334.7p while the distiller of Smirnoff vodka, Diageo, bubbled up 12p to £13.93. Having been hurt earlier this week by concerns over its prospects in Europe, Diageo was lifted by Investec upping it to "buy" from "hold." After the sale of Cadbury to Kraft two years ago, analyst Martin Deboo said that Diageo "represents what is an increasingly scarce asset in UK investing - a global leader in branded consumer goods." Outlining his reasons for turning bullish, he said the company could capitalise on a fresh round of spirits and brewing industry consolidation by selling off its "trophy asset, Guinness, that we think is both non-core and of high perceived value to alternative owners." "The 'Black Stuff" has held the marketing community, both within Diageo and without, in its mystic thrall for decades," said Mr Deboo. But he added that Guinness had been struggling in developed markets and that an exit from brewing could enhance Diageo's value and free up funds for further spirits acquisitions. Banks continued to enjoy a rebound, with Royal Bank of Scotland adding 0.38 to 27.44p. Inter-dealer broker ICAP was gaining ground too, up 13.1 to 335.7p as Bank of America-Merrill Lynch reiterated its "buy" rating. Omega Insurance jumped 4.13 to 53.88p as privately-held Barbican Insurance made a fresh takeover approach after an initial move on Omega last September failed. But Omega did not seem keen on the comeback, saying it offered "no improvement on the earlier proposal."