London's top stocks have opened lower on a weak start for the mining sector and despite some encouraging numbers from three index heavyweights.Miners are the problem, with falls across the sector led by Rio Tinto, Kazakhmys and Xstrata. Prudential is a strong performer on a report in the Times that its biggest shareholder has been moving behind the scenes to orchestrate a potential break-up of the insurer.Lloyds Banking returned to profitability in the first quarter and expects this momentum to be sustained throughout the rest of the year. The lender, 41% owned by the taxpayer, did not provide a profit figure in today's statement, but said it made a profit on a combined businesses basis due mainly to a significant downward trend in impairments. BP more than doubled profits during the first quarter following stronger than expected results from both the upstream and downstream businesses. Replacement cost profit for the first three months of the year leapt to $5.60bn from $2.39bn a year earlier and up from $3.45bn in the fourth quarter of 2009. Customers smoking roll-ups rather than branded cigarettes keep earnings momentum strong at Imperial Tobacco in the first half, despite the impact of recession in many of its main European markets. Revenue in the six months to March jumped by 8% to £13.4bn, from £12.4bn, with profits coming in at £974m versus a loss of £184m last time. Drugs giant AstraZeneca has received more good news on its cholesterol-lowering drug Crestor after the European Union cleared its use in nineteen European countries for patients at risk of a first heart attack.A big rebound by its automotive division helped engineer GKN swing back strongly into profit in the first three months of 2010. "Market conditions in the first quarter of 2010 have been encouraging and all its major businesses have continued to make good progress," it said. Premier Foods, the company behind Hovis bread, Branston pickle and Sharwood's sauces, reported a 5.1% drop in first quarter sales and said it remains cautious about the consumer and trading environment for 2010.Electrical component maker Laird said interim pre-tax profit was ahead of the same time last year as its markets continue to emerge from the depressed conditions of 2009.