Outsourcing group Serco has apologised to the British government for the "inappropriate" use of a stretch limousine to transport asylum seekers from temporary accommodation near London to Manchester, 330 kilometres away.

The luxury vehicle was used in July to pick up asylum seekers from Longford, near Heathrow airport, where recent arrivals have been held, and drive them to Manchester in the northwest.

"The transport provided, on this one occasion in July, was clearly inappropriate. There was no additional cost to the taxpayer. We have apologised," Jenni Halliday, a Serco spokeswoman, said.

Prime Minister David Cameron said last month Britain would take in 20,000 Syrian refugees over the next five years, a figure criticised as inadequate by senior judicial figures on Monday.

Asylum seekers arriving recently in Britain have included Syrians, Eritreans and Sudanese, many of them making their way to England via the "Jungle" camp near the French port of Calais.

Serco also manages Yarl's Wood, an immigration centre in southern England, under a 70 million pound ($110 million) contract, and runs immigration services in Australia.

"Our contractors are responsible for arranging the transport of asylum seekers and bear the cost of doing so," Britain's interior ministry said in a statement. "However, this incident was totally inappropriate and Serco has apologised."