Now that Progress has secured its funding, you should join it. You should join the Labour Party, you should join the Co-operative Party, you should join the Fabian Society, you should join Momentum, you should join Progress, and you should involve yourself in every way in the activities of each. You have to be in the Labour Party in order to be in Momentum, but you do not in order to be in the Co-operative Party or the Fabian Society.
Apparently, you do in order to be in Progress, but that is not my experience. Although I was not able to stand for the Strategy Board two years ago because I was not a Labour member, I was sent a ballot paper, and I used it. Get yourself sent ballot papers. Use them. If at all possible, be on them.