reference letter from current line manager? I am currently a lecturer at a UK university, and I got an oral offer from another university. I was called by their HR today saying that their official is condition on satisfactory reference checking with my current line manager, who is the HoD of my current department. In my case I do not know my HoD is willing to provide a reference letter, as I am pretty sure that he will not be happy knowing I want to leave. 

I am wondering if this (requiring reference from current line manager) is a common practices for UK universities? If there is any alternative solution to it? Thanks for your suggestions in advance.
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.