Flat rate mileage for self assessment if not car's legal owner

My wife and I share costs arising from our family car. However, I don't drive, so my wife is both legal owner and keeper of the vehicle. I'm a sole trader and my wife almost always takes me to/from places I carry out work using this car, aside from the odd occasion I use Uber. Would this allow me to claim flat-rate mileage as a travel expense on my self assessment tax return, or would I need to legally own and drive the car myself for this to be acceptable? My previous tax advisor suggested I could claim this, but it's recently come to light their advice regarding property expenses and cap-ex on cash-basis returns was incorrect so I'm concerned their guidance on mileage may also be wrong. Thanks in advance for your help.

Hi,

The car must be owned by you to qualify.

Thank you.