There is a clear economic case for opening recruitment to some jobs to non-nationals e.g. where there are skills shortages or where nationals do not want to take on employment in certain occupational areas. A straightforward immigration policy would therefore be to allow unrestricted entry to people from overseas successful in gaining such jobs.
An approach of this kind could, though, lead to levels of migration that may cause social or political instability. This is exacerbated by entry being provided for spouses and dependents of previous migrants and by any taking in of refugees.
A need may therefore arise to be selective in affording residence and employment rights (and therefore to be treated as nationals) to people from overseas. The criteria for selection should be those that promote social and political stability, therefore allowing economically beneficial immigration to be maximised without creating instability. An obvious contender in this respect is English language ability and the existence of a requirement that the English language skills of migrants be at a certain level; even if that level is higher than is strictly necessary for carrying out the job to which the persona has been recruited. Allowing entry for spouses and dependents (though not children) could also be subject to English language ability.
Surrounding all of this could be the exclusive use of English as the official language of England, with a requirement that all interactions with officialdom in England be undertaken in English. This linguistic homogeneity could both incentivise the acquisition of English language skills and provide reassurance to the native population regarding cultural continuity.