Broker tips: Shell, BP, Ashtead, N Brown

Deutsche Bank has downgraded its rating for Shell (to 'hold') but upgraded BP (to 'buy') as part of its review of the oil sector in light of the recent plunge in crude prices, now trading at their lowest levels in five years."In a sector where all are under pressure there are no easy calls. Our bias is towards those that offer improved cash flow visibility, project momentum and/or have the potential for the material change," the bank said.Berenberg has repeated its 'buy' recommendation for Ashtead, saying the consensus forecasts should rise after the equipment-rental company's strong first half."The results show that the company continues to benefit from the non-residential construction recovery in the US, take market share and improve its margin as it benefits from its scale and strong underlying rate growth in the market," said Berenberg analysts Josh Puddle and Simon Mezzanotte.A pick-up in trading towards the end of the third quarter at N Brown should please the market, according to Peel Hunt, though a 'hold' recommendation was maintained for the stock."Following a shaky start, market forecasts for the next two-three years now materially lag the picture set out in February's strategy day, an opportunity for investors if management can restore confidence over peak and deliver an accelerating performance into 2016 fiscal year," he also said.