Book review problems: to be polite or honest, that is the question...

Here's a sticky problem. I've been asked to review a book on graphic design for the 'Times Higher Educational Supplement'.

The book isn't very good - it fails to put design in any sort of context and makes some fundamental errors when it discusses things like colour theory.
I've just finished writing the review and it is pretty stinging; I'm going to sit on it for a couple of days before I send it off in the hope I can tone it down a bit.

So here's the dilemma: it isn't a book I would recommend (mind you, it's better than many out there) and it deserves to have its faults highlighted (god knows the same's going to happen to me in a few months' time!)
But the author works at a college I may want to work at soon, (indeed I do have strong links with the place already) and the publishers are ones I might want to approach myself in the near future. How do I give an honest review without shooting myself in the foot and (more conscious-prickingly) without causing major offence to a colleague?

It's such a small world...

I wonder if I can ask for the review to be anonymous? I might ring the editor later...