In reply to Flinticus:
> It has (been deliberately planted). There's a little ring of stone around it and the ground cleared within the ring.
That is a shame. If someone wanted to plant a rhododendron then there are many other much less invasive and better flowered ones to plant, though as R. ponticum is, in some places, very common it can be had for nothing.
Better to have planted, eg a larch, silver birch or rowan.
Dave