Where is the Tick symbol?

I used to hold down the Alt key and press the '3' key and I would get a tick symbol. It now produces a hash (#). How can I get my tick back!?

What do you mean by "tick"? You might go to system prefs/language & text/input sources and make sure you only have the layout checked that you want (and not two of them).

If you need the British layout commonly used on PC's, it can be downloaded here:

http://liyang.hu/osx-british.xhtml

See what shift-option-3 does. If all else fails see here:
http://www.usingmac.com/2007/12/12/100-mac-keyboard-shortcuts-for-creating-symbo ls