It seems to me both major parties are misleading the public somewhat on tax and spending.
The UK isn't a particularly high taxation state and its debt to GDP ratio isn't that high. I'm using G7 means as a comparator.
I think the arbitrary "golden rule" is either implicitly or explicitly being followed by both parties. It's a rule of thumb based upon the sustainability of debt payments, I believe, but I'm not sure it's still relevant. In short, there may be more headroom for debt-based spending than the rule implies.
Isn't the UK public's problem it wants US tax levels and Scandinavian public services so it gets a muddled neither. And that's what the parties are offering - muddle.