This is fairly common in new build estates and is frequently called "Amenity land" in planning.
Although it falls on your property, you will likely find that it is either planted with certain bushes / trees or grassed and somewhere in the covenants on the TP1 you will be unable to fence it, change the design or remove any plants.
It is a method of making the estate aesthetically nice while passing ongoing costs and responsiblity to the homeowners.
Being a new estate, check with the builder whether this strip falls under the remit of an estate management company. If so, be aware that this company will not only charge you uncapped and unregulated fees for maintaining it, but will also have full rights of access to your property and the right to evict you and put a lease on your freehold (if applicable) should you not pay.