The legislation is going to mean wood is a little more expensive to buy in the shops than previously, but also means you'll get a better burn as wood will be dryer. It's really a win-win for fire pit users: Better health & better burn with less smoke.
Lower moisture content allows wood to burn more efficiently and more completely. Besides improving health, it has many side benefits, not least reducing chimney fire risk, prolonging the life of wood burning heating appliances and getting more heat out of the same quantity of wood making it cheaper to run these appliances.
For fire pit owners it means less smokey and hotter fires when burning wood with lower moisture content. You can read my article on reducing the smoke in your fire pit here.
If you have your own wood sources there is nothing to stop you from using that wood for your fire pit. However, you need to consider the advice from DEFRA and Woodsure and be aware that burning wetter wood can be harmful to you, your family and more generally to the environment. In my experience most people who burn their own wood are well aware of the benefits of burning seasoned and dry wood and this is not really an issue for that community of users.
Smokeless Wood Burning Fire Pits
Further reading and Ready To Burn Wood Suppliers
Woodsure are the scheme administrators and have created a list of Ready To Burn certified suppliers.
You can find a supplier here: https://woodsure.co.uk/
The UK legislation has been introduced by DEFRA who have consumer publications here which explain the scheme in more detail:
Download the Smoke Control Brochure here
Download the Ready To Burn Leaflet here