I thought it was a dudd battery but a new one didn't help much.

Could it be the contact bushes? Do I need a new alternator?

Charge on battery is fine. It only happens once in 40 starts, and might sometime miraculously fix itself.

Getting tired of having to do the occasional bump start as my new place has a gravel drive and the car doesn't roll very well on it!!

 

You can rule out the alternator with a quick test using a mutimeter or electrician friend who will read the voltage off the battery whilst the engines running.
As for your starter motor could be a number of thing, wiring connections, earth. Check the soleniod on the starter should click when the igniton is turned. Could be a sticky starter motor itself.
Had a similar problem on mine sometime ago but on mine it turned out to be a faulty ignition switch.

 

Cheers.

Where exactly is the starter motor, and are they easy to get to?