By BBC Jane O'Brien BBC environment correspondent

Old bottles are being used to build British roads as a new tax, introduced this month, forces construction companies to become more environmentally friendly.

We're also looking at other waste products such as foundry sand, construction rubble and china clay waste

John Lay, RMC

The aggregate levy could cost the industry an extra �385m a year by charging �1.60 for every tonne of newly quarried materials such as sand and gravel.

One firm is cutting costs by substituting recycled green glass.

Glasphalt looks like any other road building material, but 30% is crushed glass. It does not puncture tyres because the pieces are rolled flat.

Green bottles

Aggregate company RMC has laid more than 50,000 tonnes after tests by the Transport Research Laboratory showed glasphalt performed as well as natural materials. However, there is not enough glass recycled in the UK to make it a regular alternative.

RMC's aggregates manager John Lay said: "It is a small but significant percentage, but not a single solution. We're also looking at other waste products such as foundry sand, construction rubble and china clay waste."

However, the Quarry Products Association said there was no evidence the aggregate levy would lead to better environmental practice and suggested the tax could even threaten the competitiveness of UK businesses.

The scheme is being pioneered in Nottinghamshire

In the next few years, European law will demand that Britain recycles 70% of its glass. Until recently, the target was not being met because the cost to manufacturers was prohibitive.

But, according to the British Glass Manufacturers Confederation, improvements in processing mean that 80% of green glass is now being recycled and manufacturers are struggling to obtain supplies.

Director General David Workman: "We're concerned that green glass is being used in roads because it is making it difficult to reach recycling targets.

"The problem in Britain is trying to get people to collect enough. We need more and putting it in roads is only re-using it, not recycling it."

But Valpak, a non-profit organisation that collects glass from pubs and clubs, said new markets were still needed.

Valpak's Debbie Morris said: "People need to know that their glass is being recycled in order to encourage them to collect more.

"If you create the market, you also create the incentive to collect. Using it in roads is just one example and by opening up the aggregates industry we are creating that demand."

Commercial premises have been slow to get involved in recycling because of the cost and inconvenience. Valpak is working with a number of businesses to arrange regular collections across the UK.