Sarah Gorman, who lives in Harewood Road, was taking her daughter, nine, and son, seven, to the cinema with a nine-year-old friend. They caught the 103 bus from Jennyfield to the town centre and sat at the back of the bus.

Ms Gorman said: "They turned round and said, 'Mummy what's this?' and held the syringe up. It was just lucky that the cap was on."

She quickly told the children to put it down and spoke to the driver while the bus was at traffic lights. The driver didn't act until he arrived at the bus station, when he told an official about the syringe.

Concerned by the experience, Ms Gorman called Transdev first thing on the Monday morning but said the person she spoke to didn't take the situation very seriously.

"She didn't seem interested whatsoever and she said: 'It just goes to show what type of people travel on the buses'. I said it just goes to show the buses aren't being cleaned."

A spokesman for Transdev this week said: "Although incidents like this are extremely rare, we do have a procedure in place for such an event.

"We're pleased that our staff followed this promptly. The incident was recorded, the item was handled and stored securely in the correct manner and has since been collected and disposed of by a qualified agency.

"We would like to thank Ms Gorman again for bringing this to our attention and would like to reassure her and all our customers that this was a very uncommon occurrence, but was nonetheless dealt with in the proper manner."