The British Isles are the islands of Ireland and Great Britain plus the smaller coastal islands like the Isle of Man, the Shetlands and Anglesey. Great Britain is the large Island with three co-equal and sovereign nations: England, Wales and Scotland. Along with Northern Ireland, the three countries form the United Kingdom whose formal name reflects this union perfectly, The United Kingdom of Great Britain and Northern Ireland. The UK is a ‘country of countries.’Like Great Britain, Ireland is a geographic, not a political, term. The island of Ireland incudes Northern Ireland, part of the UK, and the Republic of Ireland. Citizens of the Republic are the only ones who refer to themselves as Irish.
Few people in the UK refer to themselves as British but rather as English, Welsh, Northern Irish or Scottish. Remember scotch is an alcoholic drink, not the name of the people of Scotland.England and Wales were united as one kingdom by Henry VIII in 1536 so genealogy records are similar, if not the same, from then until now. Find them at www.nationalarchives.gov.uk or www.gro.gov.uk.
In 1707, parliaments in Scotland and in England and Wales passed the Act Union. Genealogists should note that Scotland has its own General Register Office in Edinburgh. www.scotlandspeople.gov.uk.Ireland was added in 1801 to form the United Kingdom of Great Britain and Ireland. That lasted until 1921, when the present name and configuration came into being. Some records from this 120 year period are in Dublin, even if your ancestor is Northern Irish. Sort out where specific record types are kept using the resources of the Ulster Historical Foundation. www.ancestryireland.com
A helpful video was created by C.G.P.Grey and called “The Difference Between the UK, Great Britain and England.” http://www.youtube.com/watch?v=rNu8XDBSn10&feature=relmfu With over 2 million views, it is fast paced and gives the most helpful info to sort out the terms in the first two and half minutes of its five minute playtime. Have fun.