I encounter a similar scenario fairly regularly on the way home. See
Streetmap for the location.
The B762 is a 40mph DC and I'm heading east in L1. The road drops fairly gently downhill for about 400m before the roundabout and the speed limit drops to 30mph about 100m from the roundabout. The central reservation is not wide enough to protect vehicles turning right out of Kennishead Rd to head east on the B762 - any car sitting in the central reservation waiting to complete their right turn would be blocking L2 westbound. It can sometimes take a while to get a big enough gap in both directions to allow you to safely complete the turn in 1 go.
Vehicles often turn right out of Kennishead Rd into L2 of the DC even when L1 is occupied, or will be by the time they complete the manouvre and straighten up in L2. (The Kennishead Rd part of the junction is actually so large that, in rush hour, 2 vehicles will queue side by side and cross the junction to turn right together)
When I encounter drivers turning into L2 when I'm approaching in L1 I
have to drop back in L1 to leave it clear for the turning vehicle, even if they have no intention of using it. I can't afford to risk my life assuming that they've seen me.