Accessible toilets?

I do applaud all the advancements made these days in shops, venues etc regarding disabled toilets. However, I am finding more often that these days when needing to spend a penny that you actually need to find a person who can unlock the door for you. This does not happen with the able bodied facilities. Has anybody else found the same difficulty?

I am not in a wheelchair but am disabled, from birth, and with age am finding more difficulty with walking long distances. The last thing I need is too walk around looking for a key holder if on my own. Surely there has to be an easier way?