Barrie Smith, of BSI Transport Ltd in Milton Malsor, faces fines of up to £2,000 if stowaways are found in his vehicles when returning from a cross-channel job.

But Mr Smith says his drivers are being treated unfairly because they are oblivious to any extra passengers but the blame is put on them by the border and immigration agency.

He said: "There is a major problem over there and it's getting worse.

"A lot of the immigrants are just so brazen and they're getting quite clever. It's well-organised now with people putting them in trailers and closing the door behind them.

"The driver is probably the last person to realise but he's still the one getting fined."

Mr Smith said the problem had existed for years but the methods and fearlessness of the immigrants, from as disparate countries as Afghanistan, Eritrea and Iraq, were making the problem increasingly common.

Incidents BSI had experienced included immigrants cutting through the top of the trailers and cutting and re-gluing security strips round the trailer doors.

In October driver Rob Mills was fined £800 and BSI £1,200 after two illegal immigrants were found in his vehicle at Calais.

Mr Smith said: "He felt like a criminal. They told him to stand there and not move and ended up fining him yet the two immigrants they find get a blanket round them and a cup of tea.

"The immigration authority should be helping drivers with checks, not penalising them."

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Mr Smith said several Northamptonshire firms which operated through France experienced the problem in Calais and he had heard stories about immigrants getting as far as the county without being spotted.

The Road Haulage Association (RHA) said the problem was not as big as it was 10 years ago but it could understand Mr Smith's plight.

The head of international affairs at the RHA, Peter Cullum, said: "The immigration authority says it is the driver's responsibility but that's totally unreasonable.

"They say a ladder must be carried to check for cuts in the trailer roof but, when it's cold and wet and dark in November, health and safety rules just don't allow it.

"And for a lone driver to tackle two or three immigrants just isn't on.

"I have some sympathy with drivers who get fined despite their best efforts."