For phages to be effective they will need to keep pace with bacterial resistance and be amenable to adaptation for individual patients. Genetically engineered (GE) phages may be one way of ensuring this. GE phages have already been used in the UK and elsewhere. However, if they are to be produced commercially, GE phages will need to be aligned with GMP. We recommend that the MHRA produces guidance on how GE phages will be regulated and how they will meet GMP. The MHRA should also provide guidance on how extracted phage enzymes will meet GMP requirements.