From the UN Convention on the Law of the Sea (which has some relevance to the airspace as well; Article 2 2):
PART II
TERRITORIAL SEA AND CONTIGUOUS ZONE
SECTION 1. GENERAL PROVISIONS
Article2
Legal status of the territorial sea, ofthe air space over the territorial sea and of its bedand subsoil
1.The sovereignty of a coastal State extends, beyond its land territory andinternal waters and, in the case of an archipelagic State, its archipelagicwaters, to an adjacent belt of sea, described as the territorial sea.
2.This sovereignty extends to the air space over the territorial sea as well asto its bed and subsoil.
3.The sovereignty over the territorial sea is exercised subject to thisConvention and to other rules of international law.
SECTION 2. LIMITS OF THE TERRITORIAL SEA
Article3
Breadth of the territorial sea
EveryState has the right to establish the breadth of its territorial sea up to alimit not exceeding 12 nautical miles, measured from baselines determined inaccordance with this Convention.
Article4
Outer limit of the territorial sea
Theouter limit of the territorial sea is the line every point of which is at adistance from the nearest point of the baseline equal to the breadth of theterritorial sea.
Article5
Normal baseline
Exceptwhere otherwise provided in this Convention, the normal baseline for measuringthe breadth of the territorial sea is the low-water line along the coast asmarked on large-scale charts officially recognized by the coastal State.
Mister B
(I was looking because Alec Salmond was intimating that in the event of separation from UK if the EU did not let Scotland join the club, he would deny access by EU boats (French and Spanish etc fishing types) to Scottish waters - big deal, 12 nm exclusion zone)