Harry X3

Hi there, I'm in the (painful) process of registering my Spanish X3 via the DVLA. They have asked for the engine number (amongst many other things) and BMW have quoted £400 to retrieve it from the engine block. Just before I throw good money away, does this sound right? I can't believe that something required (by what I assume to be many people importing cars) is so hard/ costly to find. Thank you very much in advance, Harry