To meet the european BRNAV requirments the unit must be approved and fitted as per the TSO so it must have a remote indicator such as a CDI or HSI ,altitude imformation from the mode C encoder (or ADC if you have one!),remote anunciators for MSG and WPT (APP arm APP active and APP arm switch for GPS approaches )and the antenna installed a set distance from the VHF com antenna , the data base must also be current.
As for the GPS approches the CAA dont seem to want to say a lot on this subject ,i think that i saw an AIC on this subject some time back that seemed to sujest that if you had the kit fitted you could do them if the approach was in the data base.
I will try to find this AIC and if i do will publish ths number on this forum.