500 foot rule and JAROPs
Yup, it does, but it also states that this may be for "a short duration". Flying at 300 feet does not necessarily mean you will break the 500 foot rule though as this rule does not stop you flying below 500 feet. It stops you flying within 500 feet of a person vessel vehicle or structure. In the UK it is difficult, in most areas, to fly below 500 feet for any length of time without doing so however! But there are large chunks of uninhabitated Britain where it is perfectly possible to do so.