vjmehra is asking about ISA investment account and what you say is stock trading, those are two different things.
Wulkan, it's never wise to comment for the sake of it, especially if you don't know what you're talking about as is evident here. You can put various investments into an ISA, two popular types being shares and other tradable instruments...
You will notice if you reread the original post carefully that the OP specifically mentions this, making your comment all the more pointlessly strange.
Terri by the way is right. ISAs, whether containing stocks or other investments are for UK residents. Hard for the Polish tax office to know what someone holds in another jurisdiction and I suspect very few Polish residents would disclose this.