clear history from shell

[Grizzly]

Hi All

I know this will be easy for most (if not all) of you but its been driving me 
mad all weekend, I have a simple script, 

#!/bin/sh

history -c && history -w && exit

each part was tested manually and the whole line has also been tested, but once 
I run the script it returns

"3: Scripts/myclean.sh: history: not found"

any pointers to what stupid error I made please