They aren't a national ID card as they are only available in a few areas of the UK.

Not strictly true if you see http://idsmart.direct.gov.uk/who-can-get-the-card.html.

Registering for updates means that as long as you otherwise fulfil the application criteria (ie importantly be over 16 years of age and hold a passport) you can get a card wherever you live in the UK. You also have to travel to one of the enrolement centres to get your biometrics done.

They can't be used as a passport replacement as no country accepts them.

Again a Timatic search for my upcoming itinerary MAN-DUB-MAN would suggest otherwise:

/ 05MAY10 / 2039 UTC



National United Kingdom (Great Britain) (GB)
Embarkation United Kingdom (Great Britain) (GB)
Destination Ireland (Republic of) (IE)


Ireland (Republic of) (IE)



Passport required.
- Passports issued to nationals of United Kingdom (Great

Britain) must be valid on arrival.
- Expired British passports endorsed British Dependent

Territories Citizen issued in Hong Kong are accepted.

Passport Exemptions:

- Holders of a National Identity Card issued by the United

Kingdom.
- Holders of proof of nationality issued to nationals of

Ireland (Rep. of) and British subjects for travel between

Ireland (Rep. of) and Great Britain and Northern Ireland
only.

Visa required, except for Holders of British passports

endorsed:
- British Citizen ; or

- British National (Overseas) ; or

- British Overseas Territories Citizen (previously referred

to as British Dependent Territories Citizen ).

Visa required, except for Holders of National Identity Cards

issued by the United Kingdom
Minors:
- Children up to/incl.16 years of ageFor details, click here
- A separate visa is not required for children up to/incl. 16
years of age, provided For details, click here
Additional Information:

- All visitors need to contact the Garda National Immigration

Bureau (GNIB) if the stay exceeds their visa free period or
their stay is longer than the period for which their visa is
valid.
Warning:
- Non-compliance with entry/transit requirements
For details, click here

I should know because I got an ID card using this method.

So apart from the name they aren't really a national ID card. BTW a British citizen has a right to enter the UK without a passport or ID card. Of course proving it might be a problem.

A similar thread - to which I also contributed - over on the BA Executive Club form - has documented evidence of fellow FTers using their UK National ID cards successfully for Intra-EU travel.

See - http://www.flyertalk.com/forum/briti...ting-them.html

FWIW, I am not concerned with the acceptability of ID cards for EU travel, as this is a moot point.

My thread centres on whether I can use my card to satisfy FR's travel document requirements. FWIW, I could use my driving licence as a UK citizen to enter Eire. This would satisfy Irish immigration (as would my ID card!) but categorically NOT Ryanair's ID/travel document requirements.