The media certainly is hell bent on discrediting Corbyn and his supporters in any way they can SH. so I take a lot of this with a pinch of salt. That there is a circle of Labour MPs who have become scared of the grass roots of their own party - this I can believe. The grass roots have been left of the parliamentary LP for as long as I can remember. All parties have tendencies and sections within them who try to guide the party in a certain way - the Tories have this as well, and with a total membership of less than 100,000 it is more to be feared with them than with Labour who have over 600,000 members. It is not allowed in the Labour Party to be a member of another party at the same time (unless the other party is abroad) - to stop people joining because of their former party membership would be highly undemocratic. In any case these other parties such as the SWP, Socialist Party of Britain etc. are all legal parties who are not (as far as I know) involved in law breaking. As long as people within the party are dedicated to a democratic route to power what does it matter what ideological identities they may have, or have had. As far as I know momentum has a membership of around 20,000 - that is around one in every 30 members - hardly a takeover, and hardly a majority amongst Corbyn supporters. If it can be proved that they constitute a 'party within a party', with their own agenda which is separate to that of the party as a whole, and is detremental to it then action should be taken. But we are very far from that scenario, and Corbyn knows this. There is more chance of the loony right taking over the shrinking, aging Tory party than there is of this.