High protein grab and go food choice

Hi everyone, I am an international student studying in London. Before I came here, I have practiced months of low carb high protein diet and it worked out well for me.

After I came to London, I found out the major stores like Costa, Pret, Greggs etc sell quick meal that's high in carb. And there's limited choice of high protein food for meal deal like Tesco.

I wonder what is the go to shops or food choice for people that takes low carb?

Your suggestions are much appreciated!