reference letter from current line manager?
It is common practice in UK universities. It would also be considered bad behaviour if your HoD was unwilling to provide a reference, or if he wrote a bad letter out of spite or revenge or similar. Of course, there are people who take it personally and are unpleasant when people leave so there's no guarantee he would be reasonable.

You should be prepared to have a discussion about why you want to change universities. Is it a promotion? Or is there a research group that is closer to your field? Presumably you applied for the job for some reason. You haven't said why you think he may not be happy. If you have been there only a short time, there might be some bad feeling. But people move all the time for all sorts of reasons.