The answer seems easy, 1 GBP = 100 GBX.
But I came across a few sites which return variable conversion value between GBP and GBX.

https://www.mataf.net/en/currency/converter-GBP-GBX?m1=1.00

Now I am wondering if 1 GBP is always equals to 100 GBX or there are some other factors involved in the conversion.