Can you use your oyster card to travel from Brentford to Ashford Surrey?

No, you cannot use an Oyster card to travel from Brentford to Ashford, Surrey. Oyster cards are primarily valid for travel within London and on services that are part of the Transport for London (TfL) network. Since Ashford is outside the London Travel Zones, you would need to use a different ticketing option, such as a National Rail ticket.