In reply to Aled Williams:
Not directly related to the question, but some information on access to the Dibona side.
We have just come back from the Ecrin. The campsite at Ailefroide was busy - but it is large and there was still some space. You cannot book a tent pitch, you turn up, register at reception and then search for a spot. Lots of multi-pitches on the nearby crags and access to some of the higher mountains.
We also drove around to the Veneon (Dibona access) side, about 2.5 hrs drive from Ailefroide to St Christophe to get access to the Selle Refuge.
There was a lot of remedial road repair going on. St Christophe was as far as you were officially allowed to go by private car, there is a small amount of parking there. When we were there the Gendarmerie was checking cars.
To get further up the road, (Dibona-Soreiller/Temple Ecrins Refuges), you are meant to pre-book online, a (free) bus that travels approx every 2/3 hours between Bourg d'Oisans to a Terminus 1km prior to La Berarde. The bus picks up/drops off, at various points along the way. The bus slots were full when we wanted to go, the local information office in St Christophe suggested we might be able to just pile on without a reservation.
Enjoy your climbing!