Is a mass socialist party possible?

Watch the discussion introduced by Derek Fraser and Ian Allinson, hosted by Greater Manchester rs21.
To achieve radical social change, those who advocate it need to be organised together into a party to coordinate our actions. In a country like Britain, such a party would need hundreds of thousands of members rooted in the daily struggles in workplaces and communities.
On the one hand, the attempt to turn Labour into a socialist party has failed. On the other, socialists outside Labour are in no organisation at all, or are scattered amongst a small groups.
Are parties with mass participation possible in an age when people have wide networks of social connections?
Is the shift from party-centred political activism to single-issue campaigning an inevitable result of the inability of parties to aggregate diverse interests?
Could a revival of working-class resistance lead to a renewed polarisation of politics more suited to a party?