Labour is the only game in town. The only realistic way working class people will gain social and economic emancipation in Britain is by reclaiming labour and reshaping it as a socialist party.
Sorry, but that's bullshit. The last time the working class tried entryism as a means of "reclaiming Labour", they were witch-hunted out of the party by Kinnock and his neoliberalism-lite centrists.
Working class people should be re-joining labour and taking their party back, its the only realistic option, talk of tiny socialist parties, anarchism etc...all pie in the sky.
To answer your question, there is no alternative.
And just
how do the working class win back a party that's changed
all the mechanisms by which constituency parties could actually change party policy?
Back when I was first a Labour Party member, I could raise any concern or issue at a party meeting, get it debated, and if the constituency picked it up, get it heard nationally, at conference, and voted on, whether that was legislative or to do with internal rules.
By the time I left Labour, they'd already started to curtail the freedom of local activists, and by 2001 they'd removed the power of constituency representatives to take matters to conference.
You're living in a dreamworld if you think Labour can be "changed from the inside". The rules and procedures have been changed to
specifically prevent that from happening, and the other two mainstream parties were so impressed at what Labour did, that they changed their own constitutions likewise.
Just to repeat: There's no mechanism by which activists can reclaim the party. All the mechanisms that allowed "people power" or "member power" have been removed.