Cheers for all your responses. Very reassuring. Had the AA bloke out (actually very good nowadays eh?! 15 minutes from call to turn up).
He checked all fuses (all ok)
Checked brakes (all ok)
Checked ABS management in engine (visually tho - and all ok)
I have normal braking so can drive it. He pointed out that if the brake warning light and ABS light is on i shouldnt drive it (as per the manual). However only ABS light on so its ok to drive. He said exactly what you all said - The sensor.
So i've got it booked in to an independent (see new 'Main Dealer - No Thanks') Thread. I'll update when I know more.