This has just been posted as a comment on my blog and I have a strong suspicion that Dafydd Robert's (who wrote it) logic is right:
The extraordinary thing in this is that surely the only governmental policy objective of such a tax would be to encourage marriage. But at what cost? This £200 per annum is going to go mostly to those who are married already, and to those who would have married anyway. There are around 250,000 marriages per year in the UK. Is it conceivable that the rate of marriage can be increased by any more than infinitesimal amount by the prospect of £200 year? If we generously assumed that 1 in 25 would be swayed to get married, then this would give us 10,000 extra marriages…at the cost of £60,000 per marriage. I myself suspect that it would be closer to £240,000 or above, and all for an almost imperceptible sociological shift, dwarfed by historical trends.
This is in fact an extremely expensive party political broadcast on behalf of the Tory party — “We’re really hot on marriage” — paid for by all of us — but with a message that isn’t even important to many (except hardcore reactionaries who think the world is going to hell in a handcart because the marriage rate is falling — How many do you know? How many do you think there are?), and disappointing to most who would take the question seriously (I mean, is this the best you could do? How about really supporting family life, via benefits and resources for people with children? Or serious money off the tax, if you must?). So what price each vote won?
The stupid party! Does anyone need more proof?