The above link (which has been cited before) clearly gives the definition of: Great Britain as England, Wales & Scotland.
UK = Great Britain + Northern Ireland
British Isles (geographical term) = Great Britain, (the whole of) Ireland, the
Channel Islands & some more islands (Orkney, Shetland, Isle of Wight, etc.)
British Islands (political term) = UK, Channel Island, Isle of Man
This link: https://www.cica.gov.uk/portal/page?_pageid=1...
gives an interesting legal definition, concerning the question whether a crime took place in Great Britain. To determine this, the definition for GB given is England, Scotland, Wales but also on a British aircraft, hovercraft or ship;
on, under or above an installation in a designated area within the meaning of Section 1(7) of the Continental Shelf Act or any other waters within 500m of the installation;
in the part of the Channel Tunnel incorporated into England as defined in Section 10 of the Channel Tunnel Act 1987.
The web address looks like a government site, and it seems to come from the criminal compensation scheme.
The following definition is from the child support agency: Definition of Great Britain (GB)
Great Britain (GB) means:
• Islands of Orkney, Shetland, the Hebrides
• Isle of Scilly
• Isle of Wight
• UK territorial waters adjacent to GB
Union with Scot Act 1706, preamble & Pt 1;
Union with Eng Act 1707 Art 1; Interp Act 78, Sch 2(5)
GB does not include:
• Isle of Man
• Northern Ireland
• Channel Islands
and can be found here: http://220.127.116.11/search?q=cache:-fTDJvxh...
"definition+of+great+britain"+&hl=en&gl=uk&ct=clnk&cd=25&client=firefox-a on page 42
So, in summary it is clear, that Northern Ireland DOES NOT form part of Great Britain, Scotland, England and Wales DO, AS DO the small Islands near Britain, but the Channel Island DO NOT.
Although admittedly, there do seem to be an awful lot of definitions on the web that lump Northern Ireland in with Great Britain, which is just simply wrong.