Have social changes since the 1950s undermined British national identity?

There is a strong argument that social changes since the 1950's have undermined British national identity. Areas such as immigration rates, the end of the British Empire and economic decline are all prime examples of this. And I will examine these areas in detail to show why being British isn't as highly thought of as it once was.
Firstly the rate of immigration in Britain has risen to unbelievably high levels in recent years. In 2001 the population of Britain was 87% white British and by 2001, just ten years this had fallen to just 80%. Also between 2004 and 2006 over half a million Eastern Europeans immigrated to Britain. This doesn't fall in with the “new right” view on what Britishness is. This view came about in the 1960's and people who shared this view believed that Britain was an island, separate from Europe which should have people with the same identity, basically that everyone should be white. Margaret Thatcher was among those who had this view and she was everything that epitomised Britishness and national identity during her reign as prime minister.
As immigration was becoming a problem for the Government, they came up with ways of restricting people entering the country because British people felt that they were too many immigrants and that they changing the culture of Britain etc. Due to the British Nationality Act, 1948, at least a quarter of the world's population was eligible to own a British passport. Due to the major influx of immigrants during the late 1940's and 1950's, the Government came up with things such as the Commonwealth Immigration Act, 1968 and the Immigration Act, 1971, to try and clamp down on the number of people entering Britain. Also they came up of these was the British citizenship test, which will determine whether someone is eligible to obtain a