Unless I am mistaken about the phasing Tim, when the pedestrian / cycle control you'll be using is on green, it'll be stopping everything from Knightsbridge / the west.
During this time, everything coming up from Grosvenor Place will be unleashed into the path you are planning on taking.
The traffic flow from Grosvenor Place doesn't get stemmed until that from Knightsbridge has a green.
It's not very nice, is it?
Yeah, that's kind of what I thought, and why I was wondering what others would say.
On reflection, I think it may be easier to just cross over HPC via the cycle path and then go along Constitution Hill and The Mall. Trying to get onto Piccadilly in the evening doesn't look too fun.
I made the mistake of trying to use the tfl Journey Plan to give me a route. It did it's normal trick of sending you along illegal routes (no right turns, wrong way down one ways etc) and suicidally busy roads and junctions.
... making it less scary than the likes of the Hanger Lane GS.
I've done Hanger Lane, it's %&#@ing scary.