You can usually use a vehicle with foreign number plates without registering or taxing it in the UK provided that all of the following conditions apply:
- you’re visiting the UK and do not plan to live in the UK
- the vehicle is registered and taxed/insured in Austria
- the vehicle is only used for a total of up to 6 months in a 12 month period (i.e. as a single extended visit or several shorter visits over the course of 12 months)
Beware: You will need to register the vehicle if you want to move it between England, Scotland and Wales (the mainland) and Northern Ireland.