I plan on taking my driving test within the next few months. I guess the rules about getting to the depot only apply once you've passed the trainee stage which takes over a year, I believe. So I should have enough time to get my licence.
Considering this advert is solely for London Gateway, then unless London Gateway has a high abundance of mentor drivers (I don’t know), it’s likely you’ll be lodged away another depots to do your handling hours.
This could include the use of a provided hire car for travel, so you might want to inform them at interview stage (should you get that far), that you don’t yet drive.