They are a group of only seven as things stand, but will there be more? And where could they come from?
The message from the news conference is that the group is open to all-comers who wish to join them. That obviously opens the door to Lib Dem MPs and former MPs and supporters who, let's face it, were damaged by the coalition with the Tories. Then there are the likes of other Labour MPs; Cooper, Benn, Reeves and so on.
It also opens the door to some members of the riven Conservative party, which is split into the ERG of 48 'known' members and the rest. I am thinking of people such as Grieve, Wollaston, Soubry, Greening, Letwin, Morgan, Clarke. Rudd etc. They are incandescent with rage at both May's leadership and the ERG.
Is a (much needed) realignment of UK politics under way? Time will tell, but what a time for it to happen!