It's definitely a London coin, but not class 1 or Henry II because the N and D are ligated (joined together). If memory serves me right that feature first occurred on class IVa, which was issued under Richard I, but the lettering style isn't right for that. My guess would be class V or VI (so John or Henry III) and judging by the position of the O of ON probably a moneyer with five letters in his name. A bit more research could probably tie the class and maybe even the moneyer down a bit.
Edit: you beat me to it Ukstu; I was glancing through my copies of Mass and Slevin for inspiration, but we seem to broadly agree on class 5 or 6.