Despite a raft of high-profile green pledges, there has been virtually no improvement in supply chain efficiencies in the food and drink industry since 2002, a survey by the Department for Transport has found.

Almost 9,000 vehicles from 39 food and drink companies were monitored by researchers on 8 March.

Most of them had either failed to meet - or had only marginally improved on - key performance indicators such as vehicle fill, empty running, delays and fuel consumption.

Of the 1.39 million kilometres that were covered by vehicles in the study, 24.1% of food kilometres and 20.1% of drink kilometres involved empty vehicles, compared with 19% for both five years ago.

The survey also found that vehicle fill had improved by just 1% in the past five years. Vehicles were on average 72% full by height and 55.1% full by weight .

Fuel consumption had also dramatically failed to be improved since 2002, with only minor improvements noted in just four of the seven types of haulage vehicles identified in the survey.

"It is disappointing that the undoubted improvement in vehicle fuel efficiency that have been produced by technical advances has not fed through to operational results," the authors of the report stated.

Traffic congestion remained the main cause of delays in the supply chain, up from 31% in 2002 to 32%.

There was also an increase in delays at compan ies' own premises, or in unloading or loading at delivery and collection points, from 50% in 2002 to 59% in 2007.

The survey's findings fly in the face of claims by food and drink companies that they are working hard to make their supply chains more efficient in a bid to reduce their impact on the ­environment.

Retailers including Asda, Sainsbury's and Tesco have pledged to reduce food miles and cut carbon dioxide emissions while, in October, the Food and Drink Federation said that all of its 211 members would back Defra's Food Industry Sustainability Strategy, which is striving for a 20% reduction in food miles by 2012.