You're confusing AWS and TPWS – AWS is the older system (based on pre-WW II technology but only deployed nationwide after WW II) which sort of roughly fits your first sentence, while TPWS will actually stop you if you're trying to pass a signal at danger (with the caveat that most automatic signals on the plain line aren't fitted on the basis that a train will relatively rarely actually have to stop at one – statistically that's absolutely sensible if you only have a limited amount of money and want to cover the higher risk signals first, but unfortunately the recent Elstow train crash did manage to hit that particular gap in the system…).
> But even then, an inquiry asked to look specifically into ATP determined we were right to reject it, it was just Too. Fucking. Expensive.
But you did eventually get TPWS which does deliver a quite large fraction of the safety benefits of ATP at a significantly smaller fraction of the costs.