You may still use your current passport with the ILR stamp to enter the UK even when you have received your naturalisation certificate. Uk citizens, in fact, are not required to have a UK passport to enter the UK. Nonetheless, It is my understanding that you only become a British citizen once you attend the ceremony. If you're keen in applying for a British passport later on, you still have 3 months from the date of your naturalisation certificate to decide when you intend to attend the ceremony. It's just a matter of timing, actually, between receiving your certificate, attending your ceremony, and the date of your travel. Hope this info helps.