When you say Ground thats the same as battery negative i assume - i.e. connect batt -ve to the same ground?

Thanks for that. I might give that a go.
Out of interest - how did you work out those resistor values or is it just an experience thing?

Oh and how do I know if its a logic mosfet? Ill be going through logic gate ICs so if I cant switch the MOSFET on 5V Ill need to use an alternative transistor (either to switch the relay or the MOSFET - see below)

Is it possible to feed a low voltage (5V) to the gate/base from the logic circuit, while passing 12V between source/emitter and drain/collector in an otherwise separate circuit?

Cheers

-- Kev