Drivers can collect spit samples to use as evidence against offenders

The bus operator First said the kits allow staff to collect samples to be used as evidence against offenders.

The samples can be checked for a match against DNA records on the Avon and Somerset police database.

The company said about a third of assaults against its drivers last year involved spitting and it hoped these attacks could be greatly reduced.

Jenny MacLeod, Bristol Area Operations Director said: "Safety is the number one priority for First and we are hopeful that these kits will act as a powerful deterrent to people spitting on drivers.

'Individual signature'

"We would urge people to think about how easily we can trace them through their DNA. It is even more accurate than a thumbprint and is similar to leaving a signature at the scene of a crime."

Alan Stewart, First bus driver and branch secretary of Transport and General Workers Union, said: "I hope with the proper training and instruction in its use, these kits will lead to a significant reduction in attacks and the prosecution of individuals involved."

Spit kits have already been issued to more than 2,000 employees working on First Great Western train services between Bristol and London Paddington.