(James Saft is a Reuters columnist. The opinions expressed are his own)

A cynical election maneuver it may well be, but Britain’s plan to impose a punitive tax on bonus payments is also reasonably well crafted and in broad terms justified.

Facing a monumental budget deficit and an election in months, British Chancellor Alistair Darling announced a plan to slap a 50 percent payroll tax, payable by banks, on their bonus payments in excess of 25,000 pounds to a given employee.

Banks can pay what they like to whom they like, but every pound a banker gets above the threshold means an additional 50 pence for the public purse. The tax will only raise about 550 million pounds, compared to a public sector borrowing requirement of 178 billion, and will expire in April, leaving delayed bonuses subject to a new higher 50 percent personal tax rate previously announced.

So, you can say it is politically motivated, that it is too small to matter and that it is subject to evasion, but these counsels of perfection ignore that it, in its own small way, will make British banks less risky, less liable to need government help and more likely to lend. It is also, given the past two years, something very like fair. Crucially it encourages banks to retain money to rebuild capital.

Banks within an insurance-based system with fiat money are inherently creatures of government; good banks outperform bad banks, the same goes for bankers, but all exist and profit because of forces greater than themselves.