What is a CHOKO? Help!

[Lucycat]

I've been given a really yummy (Australian!) book of chutneys and one of the recipes uses a choko to make a lovely looking chutney - apparantely it is also known as a 'chayote' or 'christophene'- a vegetable with a pale-green spiky skin', but does anyone know either where I can hold of one or what I could use instead?
tia

It is, apparently, a member of the gourd family

I believe it's also used in Caribbean cookery so yu should be able to get hold of it if you live a reasonable size town or maybe from an Asian grocery store if not.

OK so I need to head into Rusholme (Manchester) to find one! or Moss Side!