Self-drive car rental in Saigon

Wxx3 wrote:

I believe you must have a Vietnam driver's licence to drive a car in Vietnam.

No. UK driving licence and UK-issued International Driving Permit (IDP) is all the OP needs. (assuming he has UK car licence). See:

https://www.gov.uk/foreign-travel-advic … d-security

As of 28 March 2019, if you wish to drive cars or ride motorbikes in Vietnam you willl need to present your UK driving licence and a UK-issued International Driving Permit (IDP). If you're a long term resident in Vietnam, you can qualify for a Vietnamese driving licence with a diplomatic ID, temporary residence card or residence card validity for 3 months or more and also a valid UK driving licence or UK-issued IDP. Applications for a Vietnamese driving licence can be made at the local offices of the Department of Public Works and Transportation.

You should also make sure you have third-party insurance as required by Vietnamese law.

Don't use your passport as a deposit for hiring vehicles or in place of a fine in the event of a traffic offence.

Note the part about not leaving passport as deposit for hiring vehicles or in place of a fine in the event of a traffic offence.