last night I filled up the 306 with diesel and lost my train of thought when I noticed the pump hadn't clicked off. there was nothing untoward or leaking at this point, however there was a smell of diesel and in the car and when I got to work, it was dripping diesel. when I got home there was quite a large stain where the car had been.
now when I got to it tonight it had stopped, however it was parked level, last night it wasn't. when I stopped on way home, it still stank but no drips, but then when I got to local shop, it was dripping again at 3 drips per second. now I'm home it's still dripping.
dya reckon it's just over filled or has something gone? I can't see where it's coming from but the drip is the jacking point rear drivers side

I done 70 miles in it today and it's no better

Right you need to stop driving it until you get it sorted. Spilling fuel on the carriageway is an offence and especially dangerous when diesel as it is very slippery and won't quickly evaporate like petrol.

never found where it was leaking from.

Clean the floor and jack the car up at the front end, slide under it and see if you can see wet patches anywhere around the engine, start with that. If it's a hose it is probably a fairly easy fix and given its dripping it sort of sounds like the seal at one end of a hose isn't air tight.