Starter motor turns when finger released from button

[Jezza57]

05 Renault Megane Coupe cabriolet 1.6
What was a annoying intermittent problem which was rectified by disconnecting the battery and reconnecting it has finally turned into a major problem.
It started off when I went to start the car but all that happened was the starter motor constantly cranked the engine over without starting it even with my finger not pressing the start button and only stopped cranking when I pressed the button again. Under the bonnet a high pitched buzz could be heard but disconnecting the battery got rid of that and a click was heard as if something had reset or freed off. The car would normally start as normal after this and be OK until it stood for a couple of days it seamed. It now refuses to start at all now just the starter motor cranking over without starting the car or with finger on the starter button.
It had a new battery just 2 months ago but the battery light is on when the starter motor is cranking but did go off if the engine started.
Any ideas would be appreciated. TIA.