An armour-plated bus believed to have been used by "Iron Lady" Margaret Thatcher has been sold for nearly £17,000.

The 28-tonne battle bus, as it was known, is thought to have been built in the 1980s for the former prime minister's Northern Ireland tour.

The vehicle went under the hammer on Thursday night and beat the estimate of £10,000, selling for £16,940 to a collector, said Jonathan Humbert of Northamptonshire-based JP Humbert Auctioneers.

"There was immense interest in the bus," he said. "It sold to a spontaneous round of applause in the saleroom."

The bus, which has just 17,398 miles on the clock, has a blast-proof floor and body as well as armour-plated glass throughout, Humbert said.

It was thought to be chemical- and nuclear-proof and once had its own auxiliary generator and air supply. It also boasts a Foden chassis, a body by Glover and Webb, and is powered by a 12-litre Rolls-Royce engine.

Humbert said the bus, which has room for about 35 passengers, had come from a private seller who bought it from a research and development company, which in turn had bought it from the government.

"This isn't a good-looking vehicle by any stretch of the imagination, but it is of social and historical interest," said Humbert. "It is an irreplaceable one-off – an iron bus for the Iron Lady."