I assume that your new light fitting is metal, whereas the old one was plastic. The purpose of the green/yellow connector is to earth the metal parts of the fitting, so that if the brown (live) lead was to come lose and make contact with it, the circuit would simply fuse (or 'trip out'), rather than making the metal parts 'live'.
Unless you re-wire the entire lighting circuit (to provide an earth lead where one doesn't currently exist) you obviously can't make use of that safety feature but, in practice, you can simply connect the brown and blue leads and leave the earth terminal disconnected. That answer won't satisfy electricians who want to work strictly to the regulations but it's what I'd do (and what I know many electricians actually do anyway). Just take extra care to ensure that there's absolutely no way that the blue and (particularly) the brown wires can possibly come into contact with the metal fitting.
Chris