Top shares fell on Wednesday, pressured by integrated oil stocks as concern over the euro zone prompted fears about the demand outlook, ahead of Spanish and Italian debt auctions later in the week.

The benchmark <.FTSE> was down 37.61 points, or 0.7 percent, at 5,659.09 by 12:28 p.m., having jumped 1.5 percent on Tuesday, partly due to optimism about the U.S. earnings season after an upbeat outlook from Alcoa .

Integrated oil stocks accounted for most of the FTSE 100's weakness, led down by a 2.8-percent drop in Royal Dutch Shell , as U.S. crude futures fell by $1.

Britain's biggest energy suppliers, SSE and Centrica , meanwhile, suffered respective drops of 3.4 percent and 1.9 percent, as analysts said EDF Energy's decision to cut gas prices will force competitors to follow suit.

EDF Energy said on Wednesday it would cut its UK gas retail prices by 5 percent, passing falling wholesale prices on to its customers.

Traders said the FTSE 100 looked set to stay subdued, at least until the auctions from Spain and Italy, alongside Friday's earnings from JPMorgan Chase , the next big U.S. name to report.

Manoj Ladwa, senior trader at ETX Capital, does not see poor Spanish and Italian auctions as liable to spur a big move on the UK blue-chip index.

We are used to limited demand for these bonds and the market seems to be pricing in a 'new normal' at the moment, so I don't think there's a great propensity for the FTSE to fall.

(Editing by Jon Loades-Carter)