Hello Josselin and Graham,
Just so you know, I am back from my work trip and ready to dig into things again.
A note on British people and their respective countries: Britain is a rare case where we have "countries within a country" which obviously makes it a challenge to categorise people. I live in the UK, and I know that attitudes here vary. For example, most Welsh people I know do not mind being called "British" instead of "Welsh"; however calling a Scottish person "British" may result in a fight! :-)
To be absolutely correct in a formal sense (i.e., what nationality would the U.N. use for a person?), this is what we need to do:
Before the Act of Union in May 1707 (http://en.wikipedia.org/wiki/Acts_of_Union_1707), there was no "Great Britain," and consequently nobody was "British". People with birth dates before that should be referred to by their respective countries only. So someone born in Scotland in 1703 is Scottish but not British. Someone born in 1710 in Scotland is technically "British" though they wouldn't use that term themselves.
Now, the Act of Union only united England, Scotland, and Wales. Northern Ireland doesn't get added in until the Acts of Union 1800, which take effect January 1 of 1801. So, someone born in northern Ireland in 1798 is Irish only, but someone born in northern Ireland in 1805 is British, though again they wouldn't call themselves "British".
So, that's the history, but what does it mean for our site? I think we need to be historically correct, so eventually we need to use those two dates to write the correct labels:
Northern Ireland (before 1801): The label is "Irish"
Northern Ireland (after 1800): The label is "British (Northern Ireland)"
Scotland (before May 1770): The label is "Scottish"
Scotland (after May 1770): The label is "British (Scotland)"
Wales (before 1536): The label is "Welsh"
Wales (after 1536): The label is "British (Wales)"
Those are the labels that should eventually be standardised across the site - they will be correct, while provided the best useful information. This means to get the labels right we'll have to have birth dates in place for people, and also have their birth country tagged (i.e., not just "UK").
For searches, we'll be more lenient, so people don't get upset if their search doesn't work. Consider someone searching for all "British" art between 1750 and 1790. Before 1770, there is technically no "Britain" at all, but the average person doesn't know that; what they mean is probably "all art by people born within the current UK borders". So we'll translate that search to include Scotland, Ireland, England, and Wales, and maybe provide a historical note with the search results.
There are some other countries with similar challenges (I think that the term "Dutch" i similarly weird with some of the islands in the Atlantic), but this is the biggest case.
For now, think of the above as my "template," and don't worry too much about it until I start implementing this. For now, you can use whichever term you like - British or Scottish for example. When we get the tools in place, we'll do a review and make sure everything fits in the new system.