In adversarial politics, political parties are essentially tribes. In some countries there is a single party of the left and another of the right. Elsewhere left and right are split into factions or smaller parties which have to come together in a coalition grouping to govern.
In the England, which is the dominant country of the U.K., it remains the case that there are two main parties. Coalitions are rare, not least because the junior partners tend to get punished at the polls. Smaller parties exist and can deeply influence the political conversation. The SDP was the midwife of New Labour, and without UKIP there would have been no Brexit. But these small parties never get big, neither do they govern.
So we now have seven angry MPs who have left the Labour Party. We will have to see if the ripples of this defection get beyond the Westminster village pond. Many people may feel that the leaked intention of Honda to announce tomorrow the shutting of their Swindon car plant a good deal more important.