Government cash shouldn't be spent on trying to sway a referendum. 10 million quid is not exactly spare change either.
They did the same with the scottish referendum, so it's not that unusual.
And to be fair, 9 million quid is chump change nowadays, the govt budget would lose that amount just due to rounding, so to produce quite a glossy pamphlet and deliver it to 27 million households at 33p each, that's a bargain!
In fact knowing how private companies love to rip off the tax payer by overcharging on public contracts, I'm amazed it is so cheap!

Whether they should do it or not is another question.