well many people could easily argue that UK would not be the today's powerhouse which it is (despite Brits love slandering the UK, the country is still the most important european leader and the country with the highest per capita income - not to list that despite P-N comments Brits pay less taxes than other EU nationals) without the immigrants
some other would argue "you reap what you sew" (mispelled) because it is naive to think that the UK has no responsibilities towards some thirld world nationalities
Anyway what I am interested in it is RJM's comment, in fact it is totally misleading to attribute to Blacks that sort of crime which is daily perpetrated even by Whites. The knife culture (and the stabbings he cites) in the UK belongs equally both to Blacks and Whites.
Moving some of what you say I tend to agree with, some I do not. The most influential EU country is Germany - Germany pays more towards the EU than Britian (although Britian is second) , it has a bigger and better manufacturing and design base than Britain, it has a far superior infrastructure than Britain (ours is good but theirs is better). Germany is also represented by a leadership which looks after the interests of Germany first and foremost and does not allow itself to be "led down the garden path" by other nations as the UK has done. Germany then looks after their interests in Europe and the world with purely German interests at heart. As a German citizen that is what you want. You are correct, the UK is an influence in Europe but no more so than Germany or France for that matter.
If we are to assume your arguement that the UK does have responsibilities to other "developing nations", then it is failing in those resposibilities dramatically. Within the "Commonwealth" (read old empire which upon it's collapse, nations still wanting trade and political ties with the UK) is Zimbabwe. Robert Mugabi is a despot tyrant equal in his treatment of his people to that of Saddam Hussian. He has been in power since the 1980's, is still in power and has in fact been Knighted by the UK. Of the "developing nations" those in the Commonwealth, morally and politically the UK should be assisting first you could argue. What have we done? - nothing what so ever.
In the 1960's when Britain had a shortage of workers, Enoch Powell, a senior politician of the time, warned of the future problems of allowing almost uncontrolled numbers of migrants from the "Commonwealth" for future generations:
http://www.sterlingtimes.co.uk/powell_press.htm It is but one of his many speeches on the subject of migration and the future of the country at the time.
Regardless of his views, this led to mass migration from Jamica, Pakistan, India, and other corners of the Commonwealth. It also solved the accute shortage of labour (predominently in the lower paid jobs) of the country at the time.
These people duely had children (and these children had children etc.) born in Britain, therefore by birth being "British". The parents and grandparents also wanted to keep "home tradition" alive and not be forgotten. (No radical difference to Americans celebrating 4th July in Ukraine or me celebrating Christmas on 25 December here for example). This lead to several generations of British (via birth)/Indians (via tradition), the same for Pakistan, Jamica etc. etc.
It is every parents desire (if they are worthy of being a parent) that their children exceed their own achievements in life and therefore the children were encouraged to take full advantage of a far superior education system (1960's - 1990's) than they would have had prior to their parents migration.
This didnot immediately lead to their advancement in the workplace or society and caused the "Race Riots" of the 1980's in Brixton, Toxteth and St Pauls to name but a few.
Eventually legislation was passed to assist these people and led to these individuals succeeding in the work place of the traditional "Anglo-Saxon".
What also happened, due to many reasons, (some down to the above) was the re-discovery of their cultural past. This then divided these groups further. You need only walk around Glascow, Leeds, Bradford, Manchester, Blackburn etc. and you will now find extreme hatred between the British (with Indian roots) and the British (with Pakistani roots) in line with the international thinking of both countries today. It has indeed turned into violence along these lines on the streets of Britain both as indivduals and groups. This polarisation had led to whole communities locating themselves in particular streets where nobody but a British-Pakistani or British Indian can or will live respectively (as an example). In this respect Britian has indeed reaped what it has sewn.....but it has been magnified by international events too.
As much as the British education system is not the worst, it is not as good as it has been. There are many who obtain degrees because they have been taught how to pass the examinations without a full understanding of the degree contents. I know you will not believe that, but as an employer I can see that drastic difference between those who obtained their degrees 10 years ago and those who obtained them 3 years ago. The understanding of the subject is vastly different, to the disadvantage of the more recent graduate and the employer.
There is, now, once again, the circle coming back around (as the 1960's and 1970's generation of migrants retire) of skills shortages which is again multiplied by the lack of interest by many "Anglo-Saxon's" in studying medicine, sciences, nursing and dentistry for example and the lack of traditional apprenticeships in manufacturing and construction.
With regards the health service (for example) this is further complicated by "National Health Trusts" being accountable for every £ they spend to deliver patient care. They will therefore look to stretch this £ as far as is possible, resulting in offering work to Indian Doctor graduates (for example) who have a sound knowledge of their qualification and will work for less in many cases. It is a business "trade off" to stretch every £ against politics and fiscal policy of Government and also creates the necessity for continued migration to the UK.
The majority of posters (i think

) would not be against the migration of educated, competent skilled people coming into the UK to benefit the UK, particularly on a "contract basis" as I have worked around the world. They will be against the mass migration of unskilled and morally iligitimate migrants coming to the UK for the obvious benefits to themselves without returning anything to the UK in the short, medium or long term which past migration policies have allowed almost unhindered. Only now is the UK introducing a policy similar to that which has been in use by Australia for over a decade but as the saying goes, the horse has long since bolted and we are only now closing the stable door.
Knife crime (and crime in general) is affected by the migrants (to what degree is open to debate) due to the polarisation (as mentioned above) of communities within Britain and turns into a "turf war" between the youth/young adults from the communties. Much violence can be attributed to people from "different neighbouring housing estates" throughout the country and often (but not always) these "estates" are split along "historical migration" lines which has led to polarised communities. It is therefore not a difference between Grade A and Grade B migrants but the proximity between the ethnic groups and the "ideologies" these groups have about themselves and others around them.
The UK has a very complex problem, brought upon ourselves (with at the time little alternaive in the 1960's), which may never be resolved.