Cytochrome P450 monooxygenase enzymes are versatile catalysts which have been adapted for multiple applications in chemical synthesis. Mutation of a highly conserved active site threonine to a glutamate can convert these enzymes into peroxygenases that utilise hydrogen peroxide (H 2 O 2 ). Here we use the T252E-CYP199A4 variant to study peroxide driven oxidation activity using H 2 O 2 and urea-hydrogen peroxide (UHP). We demonstrate that the T252E variant has a higher stability to H 2 O 2 in the presence of substrate that can undergo carbon-hydrogen abstraction. This peroxygenase variant could efficiently catalyse O -demethylation and an enantioselective epoxidation reaction (94% e.e.). Neither the monooxygenase nor peroxygenase pathways of the P450 demonstrated a significant kinetic isotope effect (KIE) for the oxidation of deuterated substrates. These new peroxygenase variants offer the possibility of simpler cytochrome P450 systems for selective oxidations. To demonstrate this, a light driven H 2 O 2 generating system was used to support efficient product formation with this peroxygenase enzyme.