could anybody please tell me what the camshaft sensor actually does!!!!

The camshaft sensor advances and retards ignition/fuelling depending on the revs of the engine.
Have a read of this for the details-

[url="http://www.ignitioncarparts.co.uk/Content.aspx?page=Camshaft%20Sensor"]http://www.ignitioncarparts.co.uk/Content.aspx?page=Camshaft%20Sensor[/url]

The link provided is confusing. Be careful.

If you have a TDCI or TDDI the camshaft sensor is [b]NOT [/b]also known as the crankshaft sensor.
The TDCI has both camshaft [b]and[/b] crankshaft sensors that work together so that the ECU can determine how fast the engine is turning and the acceleration/decelleration of each piston stroke in order to optimise the fuelling
(along with a host of other sensors).

If your camshaft sensor is on the way out you will certainly have smooth running and/or starting problems.

There is a mod on the mondeo to fit an improved sensor (grey casing), and another to install a harness that improves the cam sensor voltage from 5v to 12v to strengthen the signal to the ECU.