I need a pot to regulate the power (speed) to a 12 v mini powertool,

It runs off a 12v power source and draws about 80watts.

Can anyone point to a suitable pot from Maplins

pot is a bad method of controling it TBH, you'd need an archaic wire wound pot and even then you're just binning the excess power as heat.

Coffeking,

I agree, but it works, and the issue is to slow the speed of the tool.

But what pot do i need?

It aint going to be cheap:

http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=0149007#header

Yup, as above, you need a wire-wound resistor pot that can dissipate a lot of heat. You could make your own but it wont be pretty. You could try modifying an RC car speed controller.