The UK sector of the continental shelf (UKCS) is a designated area on the continental shelf as agreed between the UK and its neighbours. It extends up to 200 miles further than the UK territorial sea. It is defined by order, currently the Continental Shelf (Designation of Areas) Order 2013 (SI 2013/3162), under the Continental Shelf Act 1964, s 1(7). The definition is referred to in the Corporation Tax Act 2009 (CTA 2009), s 1313, the Income Tax (Trading and Other Income) Act 2005 (ITTOIA 2005), s 874 and the Income Tax (Earnings and Pensions) Act 2003 (ITEPA 2003), s 41.
Activities carried out within UK territorial waters are generally treated for all tax purposes as carried out in the UK. In addition, activities relating to oil and gas exploration and exploitation that are carried out on the UKCS are treated as being carried out in the UK for the tax purposes.
This extended definition is also relevant for employment tax purposes, as employees working on the UKCS will generally be deemed to be UK resident for tax purposes.
HMRC guidance can be found at OT40550 and OT40650.