Some would look back as far as Blair for the beginning of the decline of the NHS. Even though he seemed to make gains, he did it in a way that has, long term, strangled it through fees paid to P3 providers, even today.
But whether you see that as significant or not, there is a huge feeling that Labour has abandoned working class concerns. True, they haven't been in government, but they have acted as members of the opposition, they've recommended or opposed policy, had manifestos, and so on.
In the end, this is because Labour simply is no longer a working class party. It is the party mainly of urban middle class professionals - in many ways the dominant social class. The views of most LP supporters and members and MPs reflect that, Brexit and immigration being the most clear. Controlling movement of labour, and controlling economic regulation for the benefit of local labour - the "somewheres" - has always been a huge focus of parties of labour and the working class.
The fact that many LP supporters and members think that is a crazy idea, or more often are unaware of it, and their attitude to people who think it is important, makes it very clear that the LP is now reflecting the educated middle classes - the people who overall benefit from cheap labour, and porous borders, and are not attached to any particular place.
It's really difficult to see how anyone could see them as a traditional working class party these days.