Fortunately I'm absolutely fine, and, by some fluke of fate, so - almost - is the car. I saw the deer a few seconds before I was actually going to hit it head on, and there was nobody on my right so I was able to swerve a little. Caught the deer one hell of a bang but on the left hand side of the car only.....and fortunately (for me AND the deer) Renault kindly make Clios these days with plastic front wings. The deer hit the plastic, the plastic bent inwards (cracking the paint right along the bottom of it as it went) and then pinged back out again pretty much catapaulting the deer back onto the carriageway. It knocked out the left hand side indicator, bent the mirror right inwards, scuffed the paintwork and put a small dent in the passenger side door and that - would you believe - was the only damage. The last I saw of the deer it was lying in the left hand lane kind of looking at me as though to say "Whaddya do THAT for?!" and by the time the police got to it there was no sign so presumably it must ALSO be thanking Renault for their forethought with the plastic wing thing. It was only a couple of hours before I stopped shaking.....
Today I am considering myself extremely lucky. We have a lot of deer around here and people are regularly killed or injured at far slower speeds than I was doing. For those who drive on the M25 - please do bear in mind that there are deer around the area of the M25/A12 junction...!
And thank you all for your concern!