The sorry plight of mainland children who have the right of abode in Hong Kong but who face deportation is the most recent example of a long history of uncertainty about the right of residency.
Hong Kong British subjects complained for years about being second-class nationals because they did not enjoy the right of abode in Britain.
The British Empire was extensive, stretching from Africa to the Pacific.
As the empire shrunk, successive British governments restricted colonial subjects from being able to live in Britain, fearing that a considerable number would want to reside there and the country would be unable to cope with so many foreigners.
As a result, British nationality law became one of the most complex, having to contort the definition of citizenship to exclude some categories of nationals from residency rights.
China always regarded Hong Kong Chinese as Chinese nationals because it did not recognise the unequal treaties signed last century, which ceded and leased Hong Kong to Britain.
Chinese nationality law distinguishes itself by adherence to bloodline, and it is almost impossible to divest. China used to claim overseas Chinese also as its nationals.
Since the 1950s, China has had many tense moments with Asian neighbours because of this claim.
It had to enter into a series of diplomatic negotiations with Asian governments with large ethnic Chinese populations in order to let go of the people it claimed as its own by reason of blood.
The children's plight provides an additional twist to what is already complicated. The Basic Law - a Chinese law specially devised for the Hong Kong Special Administrative Region - confers permanent resident status for the first time on any Chinese national born outside Hong Kong to a parent who is a permanent resident.
As a result, the government estimates that about 66,000 mainland-resident children who did not previously qualify as permanent resident now do so.
Hong Kong introduced an amendment ordinance on July 9 to impose immigration control on these children.
The new law does not deny they have the right of abode but it stops them from exercising the right until their permanent resident status is 'established'. To do so, a person must hold either an identity card or a 'certificate of entitlement'.
This may sound a reasonable procedural requirement on the surface, but it is not.
The irony is that they cannot apply for ID cards because the law excludes this option.
This means these children must rely on getting a certificate of entitlement.
This certificate must be affixed to a valid travel document, meaning in this case, a one-way exit permit issued by the Chinese Government.
In effect, Hong Kong law renders it impossible for these children to exercise their right of abode here until they get a one-way permit from China. Eligibility for these prized permits does not depend on the fact that the Basic Law gives these children the right of abode in Hong Kong.
Any person waiting for a permit to be issued in China is treated by the Hong Kong authorities as an unwanted immigrant.
He or she cannot land here and will be forcibly repatriated if found.
Indeed, authorising the immediate removal of children who are already here is a principal purpose of the new law.
The Government had better think about how to cope rather than create unfounded fear of catastrophe among Hong Kong people in order to support what it finds administratively convenient.