If the customer is always right, the "Big Six" energy suppliers ought to be in deep trouble.

Few respect them; few trust them; and precious few are impressed by their responses to a precipitous collapse in world oil and gas prices. Homely image-building through relentless advertising fools no one.

Not for the first time, the annual Which? Survey of customer satisfaction should cause consternation in corporate public relations departments. Past experience says, however, that any discomfort will fail to transform behaviour. This is the fourth year in which the six have earned the contempt of customers. Clearly, they have not changed their ways.

If you score just 35 per cent for complaint handling and customer service, you have a problem. That, though, is the dubious distinction awarded to Npower, closely followed by ScottishPower (41 per cent), EDF Energy (49 per cent), British Gas (49 per cent), E.On (50 per cent) and SSE (50 per cent). Remarkably, ScottishPower and Npower have even managed to under-perform an industry average dragged down to 48 per cent by their lacklustre peers.

Small operators meanwhile shine, from Ecotricity with a score of 84 per cent to Flow Energy on 73 per cent. A clutch of other companies stand within that range. It suggests, first, that rankings for the Big Six are no accident; secondly, that the advantages of being a corporate giant are overrated, both for customers and the companies themselves.

For the former, much would be forgiven if bills bore a relationship to reality. Oil prices have declined by around 55 per cent in the past six months. In tough times, when the cost of domestic electricity and gas was rising relentlessly, the Big Six never tired of explaining the inter-relationships between global energy markets. Now all the tales ring hollow.

ScottishPower will reduce prices by 4.8 per cent, but not until 20 February, when consumption has begun to decline. British Gas will cut by 5 per cent, but not until 27 February. E.On has at least already implemented its 3.5 per cent reduction. None of these offers compares, even remotely, to a fall in wholesale gas prices of fully 20 per cent since November.

Even now, the Big Six persist with the excuse that they bought their supplies last year, when prices were higher. In simple logic, this means only that they have a big guaranteed windfall in prospect, one that could be passed on in full to customers.

Certain of these firms, such as British Gas, also neglect to mention that their parent conglomerates - Centrica in the case of British Gas - are active as both buyers and sellers of energy. In essence, they sell to themselves. Those who make markets should hesitate before blaming market forces.

If not, the six might not be quite so big for much longer. The Which? Survey is more than a confirmation of what too many customers already knew. It counts as a warning. The temperature of opinion, if not homes, is rising.