I'm thinking a a small majority if it's a 1991 'Khaki' GE similar to 1992 due to the poll tax . . . but still bye bye to Kinnock, thus making Maggie safe.
But if it's a 1992 GE with John Smiths 'tax & spend' manifesto I'm thinking of another 1987-ish majority with an earlier entrance of Tony Blair as PM after their 1992 defeat avoiding John Smith as leader. The Labour manifesto would've been meat and drink to Maggie T and thus scuppering any chance of the 'wets' getting rid of her.
I'm just curious how future EEC (later EC) relations pan out and how effective in the 1997 GE would a Labour Party be against a possible Maggie led Govt.
From my memory of the period (and this is the memory of one person, so I am not claiming any great objectivity).
By 1990, Thatcher had moved from being an electoral asset to being an electoral liability. A big electoral liability. After the Poll Tax fiasco, things had gone downhill. Because of Thatcher's style of leadership - basically taking control and being the one in charge (delegation was never her strong suit) - meant that the Poll Tax fiasco was directly attributed to her personally. Polling suggested that Tory support was plummeting.
That was the whole reason why the Tory party kicked her out. Loyalty is not the strong suit of the Tory party.
Now, one can posit one of two things: the Poll Tax fiasco never happened. Maybe it was adequately funded with the intention of decreasing the funding later, so that people newly paying (ie, those who hadn't previously been paying rates) saw rather more modest tax bills. Maybe it was never introduced. In the absence of the Poll Tax fiasco, Thatcher is less of a political liability (although her value as an electoral asset is still going to diminish). In this case, the Tory Party is less likely to dump her overboard.
Or maybe she somehow survives the leadership election.
The two options will give different outcomes. In the first, the Tory Party will be less damaged in the polls than they were OTL. In the second, it will be much more damaged. So the first thing one has to do is specify how she survives to retain the leadership. If one goes down the second route, there is basically no way she wins an election in 1992. We are looking at a Kinnock victory. In the first, it depends on circumstances at the time.
That's your first decision point. How does she survive as leader?