It should have a label somewhere giving the Voltage, current draw and supply frequency.

If in doubt, don't plug it in.

My Apple IIgs wasn't dual voltage, I think it's quite likely that a Mac SE wouldn't be either.

A step-down transformer is the safest option.

As has been said, you need to determine what its supply needs are; don't just plug it in unless you know it takes 230V. If it's a 110V device you will do damage to it - you would need a stepdown transformer (or some other device that can serve that function; some power rengerators, for example, can do voltage conversion) to connect it. Alternately you may be able to buy a power supply for it that takes 230V and replace the one it currently has.

Thanks for your help guys, I went out at lunch time and got this from Maplins.

http://www.maplin.co.uk/p/maplin-230v-to-110v … converter-vr05f