Update
Re my previous post, the availability of the "1 million" flights is now showing. As the Bean Counter says, it's Tuesday & Wednesday only, and for three months (Apr-Jun).
The number of routes showing this fare available is very small, with only four routes (out of 94) from Stansted, 5/35 at EMA, 2/42 at Liverpool, 1/13 at Luton, 4/20 at Bristol, 11/84 at Dublin, and so on.
I still question whether this amounts to anything like 1,000,000 seats.