I'm not sure how EY works, but I'm pretty sure it'd be similar to our firm whereby engagement members should aim to use public transport, but if it's not possible or viable, then use taxis (which are reimbursed). Driving oneself is usually not the preferred option and requires approval from seniors (as the firm has to reimburse the mileage), but in some cases (such as clients in rural areas)- it's the only way. I think it's unlikely that they'll send you out to somewhere rural without either someone else to take you there, or knowing that you're capable of driving there yourself.
In short, having your license is definitely an advantage (I often drive out to clients who are near me, but nowhere near public transport) but isn't a necessity.