I suspected this was the case. However, as the bay isn't clearly marked (the words 'LOADING BAY' are worn away), could I appeal on these grounds? Thanks

Hi, Today I received a parking ticket for being in a loading bay and the officer didn't see any activity for 20 minutes. I was away from my van, delivering to my place of work. I was asked to wait for some goods so I did. I was away from the van for no more than 25 minutes. When I returned, I had a ticket. I was using the bay for the correct purpose. I have done for the last 3 years and never had a ticket before. I want to appeal but don't know if it's worth it. I have to pay the fine myself so don't want to pay the full amount. I checked the loading 'bay' and found that the road markings saying 'loading bay' are no longer legible on the road as they have virtually worn away. The sign simply says 'loading only', but doesn't specify a time limit. It is my understanding that the road markings have to be clearly visible. They aren't. Do I have a case? Has anyone contested a similar fine? Any help or advice appreciated. Thanks, Louise