There's a cat with a very similar description been hanging around Birkenhead Central station for a good few days now. Not saying its the same cat but it does look very out of place there. I've seen it by the fence on Argyle St South, scavenging on the platform and sat inside the builders merchants opposite the station. I couldn't explain how your cat may have got there but cats do the strangest things. (climb in the back of vans, lorries, i even saw one get on a bus many years ago in Wallasey. Didn't even buy a ticket.)
As i said, i'm not saying it is yours but it may be worth checking around that area if you can. I last saw it on Tuesday, i've beeen off work since.