FYI memorizing 112 is probably a better idea. It's baked into GSM spec and gets redirected to the right country end-point (like 999 for UK) in most of the world.
Same difference while in UK, but good habit for travelling.
For my experience, when possible it's better to use the more direct number – that extra layer of redirection takes only a minute or two, but in an emergency that can be a lot.
How can a redirection take minutes?! And do you at least get some relaxing elevator music for you to remain calm while watching your house burn down?
Nah, I don't mean just the "please hold the line." But most of all redirection means that you need to explain the situation to two different operators before the response is sent.