amps, volts and mains switches

I'm sure I should know this, but it turns out I don't. I'm looking online for a new switch to fit in the mains cable of my printer power supply. I use the nice LED lighting ones.

I vaguely remember how power supplies work, but I can't remember the maths. If my printer is using 30A at 12V, what rating mains switch do I need? Mains voltage here in the UK is 230V, so what amps should it support?

Thanks