Yes. At a house, decking is only permitted development if it's no more than 30cm (300mm) above the ground, so a deck over that line needs planning permission before you build. At or below it, covering no more than half the garden together with other extensions and outbuildings, and with nothing in front of the house, no application is needed. Flats, maisonettes and listed buildings don't get these rights at all.
That 30cm line matters more here than in a flat inland town. Alum, Middle, Durley and Boscombe chine gardens, and the gardens stepping down toward West Cliff and East Cliff, rarely sit level, so a deck that looks low from the patio door can sit well over 300mm above the ground where the garden falls away. Get the measurement checked before you commit to a design; my decking planning permission page covers the BCP rules in full.
Where is the 30 cm measured on my sloping or chine-side garden?
The rules don't answer this one cleanly, so check it for your own garden. The government’s permitted development technical guidance measures height from ground level, says ground level “would not include any addition laid on top of the ground such as decking”, and says that where ground level is not uniform, “the ground level is the highest part of the surface of the ground next to the building”. It doesn't say how that applies to a deck that's level with the top of a slope and high above the ground at the bottom. If any part of your deck will be more than 30cm above the ground beneath it, get BCP Council's view in writing, or apply for a lawful development certificate, before you build.
Does my lease or freeholder consent still matter if planning permission is not needed?
Planning permission and your lease are two separate questions, and clearing one does not clear the other. If your home is leasehold, or a freeholder's covenants restrict what can be built in the garden, that consent sits outside Permitted Development entirely and needs checking against your own deeds. Check your lease, and your freeholder where one exists, before work starts regardless of what the planning rules allow.
If you want a straight answer for your own garden, ring Alfie on 01202 144040.
Related: back to planning permission for decking and pergolas: the questions Bournemouth homeowners ask.
Related: do decking permitted-development rights apply to my converted flat or maisonette?
Related: raised decking on a sloping garden