Jupiter wrote:
In Britain people look strangely and say that they have just brewer
yeast. Is it the same thing as nutritional yeast?

No. They're very different, and not interchangeable.

Second question, where I can get it in Britain?

Mail order or shop?

PS. I do not have a vegan cat yet. In fact, I was just researching
possibilities if it is possible for cat to be a vegan.

NO. I realize there are some people who think cats can be vegan, but I
find it morally reprehensible that such people arrogantly force their
alternative lifestyle values on a helpless creature nature has seen fit
to live by its own specific set of values. Cats do not eat rice and
beans. They eat fish, mice, meat, and offal. Please don't go so loopy
into veganism that you project your peculiar sensitivities onto other
helpless species.