On option (3) would certainly have been possible if factors varied, particularly if Thatcher's relationship with the wets somehow came too unstuck and you tried to bring the monstrous ideological homunculus that was Michael Foot's Shadow Cabinet or its functional equivalent into actual power (lots of serious lefties, odd ducks like fire-eating anti-European Peter Shore who was to the right on everything else, the practically Tory David Owen, old like high-functioning Liberals like Bill Rodgers or a comeback from Woy, Labour Right stalwarts like Healey and his proteges like Hattersley, and so on.) I have a nugget in a TL I'm working on now with a Thatcher govt from the mid-Seventies that gives out over a different foreign-policy crisis in '79 and stuff... happens wrt Sunny Jim so he's out of the picture, and from the back benches clamoring as the voice of "the common Labour supporter" Mrs. Castle herownself plays the various not-Healeys off each other until she builds a wafer-thin victory under the old MP-vote system claiming to be the only one who can hold this body of the left that's no longer really an ideologically coherent party together. This results in a Labour government of all ideological stripes -- people like Benn and Eric Heffer have significant though not Four Greats level briefs, rightists like Hattersley and Varley are also mid-level strivers, you have Healey as deputy back at the Exchequer, Shore as IOTL's shadow world Foreign Secretary busy trying to get the hell out of Europe, Owen at MoD threatening fire and brimstone if they take his SSBNs away (though he'll tolerate some trimming of the "gravity" bombs), and a party that once they're over the initial national hump that brought them in (by a coup d'état confidence vote staged by wets trying to human-wave Thatcher like Caesar's assassins) is absolutely ready to tear itself apart over every issue -- liberal versus state economics, Europe versus protectionism, Ulster, Polaris, democratizing (sorry, "democratising", must remember the audience here) the unions, what to do about Militant, on and on. And in that case Owen leads a small walkout that effectively doubles the Liberals and as talks for bilateral arms reduction stall with a reactionary Soviet government (who don't want these puffed-up would be socialists disarming because it just means Washington will take it as an excuse to escalate its nuclear options and unbalance the balance) and there are issues with the economy, Benn gets in a snit and leads people like himself and Heffer and Skinner and Atkinson etc. out to a "Democratic Socialists" party (eh? eh? Parallelism all week, tip your waiter ... *taps mic* is this thing on?) Could very easily have happened at any number of points that you had right and left hive off of the whole. And all things considered it was likelier that you'd have a small but more durable presence to the left depending on constituency-party dynamics (especially through the Eighties and into the early Nineties because these particular constituencies are then going to be absolute honey pots for entryists.) Otherwise it's mostly the hard-core folk on the right abandoning for the Liberals directly without a Social Democratic phenomenon and indeed, just perhaps, more chance of people of that disposition (paging Mr. Ashdown...) joining in and rising in the party and keeping the neoliberal entryists like Tony et al. from dominating the coming generation.
Also you could have an outbreak of "green realism," a kind of "Green Right" that posits some level of baseline defence spending, qualified support for certain kinds of liberal interventionism (ex. Rwanda) and so on, but that otherwise becomes the socially-ultra-liberal, environmentally driven, functionally socialist alternative to an essentially Blairite Labour, pulling a lot from the left (but keeping a watchful eye on "personalities" like Skinner and Livingstone, who could be wreckers if let loose in the mechanisms of party governance and alienate potential voters) but also from the more social-democratic Lib Dems as well, and growing towards a sort of ungainly but decently-populated amalgam of the German Greens and Canada's NDP.
I could see either of those really, "Green Pragmatists" winning lefty converts from Labour and Lib Dems as they go on their "but my dear friend Peregrine told me The City is simply top drawer" neoliberal jag, or instead an Eighties fragmentation with a fundamentally Bennite, Campaign Group-based party splitting off the left just as the Gang of Four did from the right.
ETA: Die Linke is perhaps the best contemporary analog to the "Eighties option." You've got a mix of "soft" Marxists from the old DDR, a mixture of doctrinaire socialism and cultural populism preached in particular by an extremely talented and combative former leadership figure of the SPD (Oskar Lafontaine) frustrated in both this policy goals and his dreams of longer-term leadership when he was dished by Schroeder, forming a party out of the hard SPD left and those further out and promising to be more ideologically "pure" than the more pragmatic Greens. Sounds about like the BennsorryDemocraticSocialists to me.