Lights and evrything electrical fine, full of petrol, but when l turn key it makes a noise for about 1 second then cuts out dead

Your problem is bound to be solved here!

http://206info.co.uk/ForumsPro/viewforum/f=4.html

l would say that ur solenoid is dead. The solenoid does not give electricity to ur STARTER MOTOR, by properly becoming an electro-magnet that pulls the starter motor into a meshing gear with the flywheel.
l speak from years of experience. Unless something else is drastically wrong, from ur two sentences, l give u my educated opinion.

The test for this is: have a friend start the car for you, while u gently tap on the solenoid with a wooden board. The vibration to the solenoid may give u one last success. BUT! the 206 solenoid is difficult to reach.

Another dangerous test (not recommended, except for MYSELF) is to roll the car down a hill, & with the key ON, try to pop the clutch & roll start it. Ha ha, l am not even sure u can do this with a ''modern'' car anymore. If this test fails, u r at the bottom of the hill.