I think JAM stands for Just About Managing... or the squeezed classes.
There are so many thoughtful and thought provoking posts here, so just adding another that I hope will offer light not heat.
The Today programme had a section about 6.20 this morning about polarisation, driven by globalisation in which one of the speakers commented that the global corporations now escape effective regulation in any country and evade moral obligations to employees and society (such as paying tax). Politicians' collective failure to force corporations to act responsibly towards all, instead of just shareholders, is what allows them to off-shore jobs to lower wage economies. Communications and systems technology enable financial whizzkids to send the money to the states imposing the least legal and taxation burdens.
And, to a degree, the emergence of English as the world's second language for any person to be considered "well-educated" has meant that English speaking countries have suffered (and will suffer) disproportionately. For example, calls to telephone service centres can be handled in India or the Philippines as effectively and much cheaper than in Southport or Scotland. Perhaps rather more than countries like Germany or France, whose languages are spoken less widely and where there are fewer opportunities to send the work somewhere it can be done on the cheap.
And if there are fewer well paid jobs, then the tax base shrinks, forcing economies in public services just as the need for them explodes.
I can't buy into either the left or the right wing extreme views sometimes put forward on these forums. There's an old saying: If you are not a Communist when you are 18, there's something wrong with your heart; if you are still one at 48, there's more wrong with your head. Which is code for it's impossible ever to level the playing field completely but it's not an excuse for not trying. Poverty is always relative but one measure of a good society (or government) might be the amount which is tolerated.