Your 'already crowded island' has a population density of 267 inhabitants per square kilometre - just for the sake of comparison the Netherlands has 393. Despite this the Dutch have some of the highest living standards in Europe, and manage to be the highest payers into the EU. (per head of population). The problem is that the UK. has become used to migrants from countries which had a prior connection to the UK. and who, as a result, spoke some English on arrival. This was different with Poland and Rumania hence the problems of integration - Germany has experienced nothing but language problems since immigration started in the 50s, yet the post war boom would have been impossible without it. It is not a question of 'numbers' alone - it is a question of keeping a demographic balance between working population and non working population. The major problem is that you classify all immigrants under the label of 'desirable' or 'undesirable' - the only undesirables are those who have been convicted for a criminal offence, and Britain can turn them back already. Other than that, all you need is a language course, and to treat people like human beings, and anybody can become a 'desirable' and a benefit to the country.