You will end up on the NIR if you take a Biometric Passort but may not necessarily have an id card as the government has claimed this is for UK residents only.
Tony Blair requested from the EU Court that Britain was included in the creation of the European identity database (SISII). Prior to this British subjects were immune from inclusion.
The ID Card Bill makes allowances for the NIR to be populated with information from other databases. Information from SISII can be used to build your NIR profile. UKPA databases are likely to be used to populate the NIR anyway as one of the key arguements is to prevent illegal immigration.
Despite growing awareness of the ID card there is still significant ingorance of the threat of the biometric passport. Political attitutudes towards the biometric passport are schizophrenic. The Libdems and Tories, whilst opposing the id card have supported the biometric passport. They don't want a UK biometric ID system, but are quite happy for an EU one.
Also be aware that the cost for an ex-patriot often exceeds that of a UK resident. You and your family need to attend an identity interview at a designated consular office or embassy, you must bear the cost for this; for example, ex-patriots in the SW of France will have to travel to Bordeaux or Paris.