Hi Ash, good luck with your visits, I would imagine Crewe would be much busier.
With modern locos, the first two digits of the number is the class. So if you saw
60056 it is a class 60.
Try googling "class 60 loco" and look at the Wikipedea entry, it will give you the basics, then other web sites could give you more details.
https://en.wikipedia.org/wiki/British_Rail_Class_60