In your own terms, you were 'granted this'. This goes against a potential claim that you might have had for a claim on the land by Adverse Possession' - the interpretation that you are putting upon the 12 year rule.
Claiming land under Adverse Possession may apply when you have taken possession of, and maintained a piece of unregistered land for more than 12 years, after which it is possible to claim the land as your own.
The rules were changed in 2002 and for registered land (registered at the Land Registry, that is) it is pretty impossible to register absolute title.
Don't get confused between the council's 'planning officer' and ownership of the land - the Land Registry controls the latter - planning is to do with what structures can be built on the land.
You need to see what the Council has registered in the councils' title at the LR here.
http://www.landregistry.gov.uk/www/wps/portal/ !ut/p/c1/04_SB8K8xLLM9MSSzPy8xBz9CP0os3gfN1MTQ wt381AP0xAXAyNzCw9jsxBnYwN_M_1wkA68KgqysxUBKVJ ImQ!!
If you find it is still owned by them, offer a nominal sum - if the piece is of no practical use to anyone else.