Police are appealing for witnesses to the theft of the FedEx Ford Transit, which occured in Linley Road on Thursday at 10.30am.
The driver had stopped to make a delivery and when he got back in the van, he was pulled out by the thief.
He managed to cling on to the side window as the van was driven off by the thief - only letting go when he thought he may collide with a car travelling in the opposite direction.
The van, which has the registration number WL05 FAU, is believed to have driven off down Welsh Road West.
The delivery driver suffered a cut to his head requiring treatment by ambulance paramedics as a result of the incident.
Officers carried out house to house enquiries and made an immediate wide search of the surrounding area. The van was later recovered by police near Napton church.
The thief is described as a slim white man, approximately 5ft 8ins tall, with short ginger hair and dressed in blue trousers and a blue jacket. He is thought to be in his 30s and spoke in a foreign language – possibly eastern European.
Police are investigating whether the thief had an accomplice who was watching the robbery from a car and may have followed the van.
Officers are are warning courier drivers to be vigilant and to be aware of vehicles around them as they make deliveries and to remove the keys when making deliveries.
Witnesses are please asked to contact PSI John Eaton on 415000 ext 4070 or independent charity Crimestoppers anonymously on 0800 555 111.