In message , at 07:53:25 on Wed, 19 Jun
2019, Recliner remarked:

They'll build the diverted, sunken, bridged M25 to the west of the
current road, with no disruption to road or air traffic during the
building, which might take a couple of years.

The only disruption will come at the end, when the traffic is diverted to
the new route. My guess is that the northbound traffic will be moved first,
with a few weeks of lane 1 closures required while they connect the new to
the old carriageways, then an overnight closure for the final switch to be
made. The same procedure would then be followed a few months later to
divert the southbound carriageway to the new alignment.

The amount of work you would be expecting them to do "overnight" beggars
belief.
--
Roland Perry