Ed Balls has bought out that good old political trick of higher taxes on the wealthy. As we all know, taxes on someone else are always a vote winning idea.
As the saying goes, if you rob Peter to pay Paul, you can normally rely on Paul's vote come an election.
What is harder to dispute is that 50% is above the Laffer curve. the report from the Treasury thus far is pretty inconclusive. Due to people shifting their incomes, in collusion with their companies, in 201/12, there is little real data to work on. We don't really know if lowering the tax threshold raised more money or not. Equally, due to the timing int he middle of a dreadful recession where tax receipts collapsed, we don't really know if it raised any either. Truthfully too, no one knows where the Laffer curve is or if it even exists; if it did real events will always interfere to skew the results anyhow.
The best that can be said is that in the round of £600 billion odd of public spending, the difference is a rounding error. But of course, politically, this is a good old piece of divisive us-against-them vote-winning.
For Labour, it smacks of desperation as they are opposed to every cut so need some sort of veneer to say they would raise revenue. For the Tories, they are left on the side of big business and 'the rich' - a homely pace but not one packed with voters (although election funding is at least sorted!).
Worse news for those of us who want to vote UKIP. Their policy of a flat tax has also had real problems in the real world. Most of the EU Countries who have applied it also have an equivalent of National Insurance too. Except that the NI is often 30%+, so the nice flat tax of 10% ends up equating to 40% odd anyway.
You just can't escape the need to tax in Countries where social spending is so high and increasing all the time as the population grows and ages.
Personally, I think this is great politics from Labour - useless economic policy, but then they have that mark anyway, it hardens their anti-rich vote which outside of SE England is the key to power for them.