The politicians are flawed, but thats a function of humans in a position of power and not something thats going to change. Like you say, the system prevents them being able to make radical changes.

I guess the problem with a 20 year period is that it spans a whole generation, so the knee jerk reaction would always be a change in leadership at every election.

Quite possibly I am wrong, who knows, labour might get another term, but if someone doesn't do something about this countries spending (ironically similar to the credit card wielding "I'll pay for it tomorrow" general public then things will only continue to worsen.