Why is there an SSPCA?

I have never understood this.

The Scottish SPCA is picking a fight with the Royal SPCA over who should donate. The SSPCA says that Scots should not donate to the RSPCA because they don't have a Scottish remit.

So my thought is why have an SSPCA? Why is there two almost identically named charities with the same goals serving different geographical areas? It seems to me that this is duplication of effort. Why pay the money for similar command structures? Surely this is duplicating expense and that is money not being spent on sick donkeys?