Ethnicity is "broadly equivalent, only differing" in Scotland and England

More Census ethnicity nonsense (thanks to JD!).

To ask Her Majesty's Government why the 2011 census question on ethnic group in England and Wales had five options for "White" when the Scottish version had nine options which included Polish, and has a different wording for Gypsy or Irish Traveller which excludes the word "Irish"; and how overall United Kingdom figures will be calculated and displayed given those differences.[HL7713]

A  very good question, not very adequately answered:

In England and Wales the form and content of the ethnicity questions have resulted from extensive consultation with users and other key stakeholders as part of a formal consultation exercise on census topics....blah, blah, blah.

Whereas:

In Scotland, a wide-ranging review of the way that ethnicity was classified was undertaken following the 2001 census, to ensure the development of a classification for use in Scottish surveys that reflected modern circumstances, met users' information needs and had broad community support... blah, blah, blah

So, to summarise: in both cases, extensive research into the issue was apparently done.

The "White" categories are broadly equivalent, only differing, in Scotland, in the addition of a "Polish" category-where this group form a significantly larger proportion of the ethnic minority population than in England and Wales, justifying a separate tick box-and a separate category for "Scottish" to provide consistency with the 2001 question. The omission of "Irish" from the title of the new "Gypsy/Traveller" group reflected particular sensitivities to the wording of this category in Scotland.

So, to summarise: whereas it is possible to define yourself as a "white Pole" in Scotland you are simply, I guess, "white" in England because there is proportionally less of you there.
You also may not be an Irish Traveller in Scotland as the word "Irish" is more sensitive north of Hadrian's Wall than in England. Have I got it right?
 
For the Census to have any meaningful value whatsover, shouldn't there be a "consistency" between the different parts of the UK as well as with the previous local versions?