Mystery possibly Roman can anyone help?

Have had this coin a while. It was discovered in Norfolk, England. It looks Roman but I cannot find any reference.

can anyone help please.

Cheers.

https://en.wikipedia.org/wiki/Saltire 

 The shield with X in middle looks like Saint Andrew's Cross 

but Scotland is a long way from Norfolk. Does not look Roman. 

 May not be a X and could be crossed keys instead. 

Thank you for your input. I will investigate those possibilities further.

Thank you.