She'll be settling in Wendesday anyway, I imagine she'll just venture out to record, the recording studio she used last time is no where near Westminister where they'll be likely to be marching. Should be fine...don't let it ruin your time in London.
You can see all flights from Tokyo to London here-
http://uk.flightaware.com/live/findf...2C+England%29+
She's either failther Virgin Atlantic, Japan Company or All Nippon I think.