That's a USB charger. What you want is a US-to-UK plug adapter for the charger that came with the Macbook. Something like this:
http://www.amazon.co.uk/Travel-Adapt.../dp/B003TOS786
To be honest, though, if you're planning to use this permanently in the UK, I'd bite the bullet and buy a new Macbook charger from Apple. Plug adapters aren't really intended for permanent use.