Firefighters were called to Halden Road at just after midnight on August 4 in response to a 999 call reporting a bus on fire at the roadside.
The fire was extinguished and no-one was injured.
The fire was believed to have been started deliberately and police were notified.
Police said that the single decker party bus was parked on the street and left unlocked.
Someone got onto the bus and a fire was started deliberately, causing £3000 damage.
Anyone with information should contact police on 101 quoting crime reference number WB1606231.
Thanks to John Corcoran for the photos.