Kings Cross to Cambridge: how nasty can a journey get?

I am afraid that this post will have most to say to those who travel by train between Kings Cross and Cambridge; but I suspect that my story will resonate with most other people who use London commuter  lines.

OK, first off Kings Cross -- and, I guess, a minor quibble. The underground station there serves both Kings Cross and St Pancras (now the Eurostar terminal). Until a few months ago, if you came into Kings Cross on the mainline train you went straight down to the tube -- and, within...