I agree with this but can you see it happening any time soon? Just read the politics threads on here as well as other mainstream leftish thought and the answer becomes quite clear, and not in a good way.
If anyone is at a low point in their life and wants me to recommend them some reading, Nick Cohen's "What's Left?" deals with this subject really well I think, even if its about 15 years old.
Cohen's is a pretty good book, as is Pascal Bruckner's even older and even better book 'Tears of the White Man', which deals (from a left-wing point of view) with the problem of the 'self-hating' Left in the context of what he calls 'Third Worldism'. That's the philosophy which says things like..."Mugabe on the rampage, killing his opponents? Must be our fault" or "Another Islamist attack on Manchester? What did we do wrong?" Both books are provocative and flawed, but both - especially Bruckner's - are real eye-openers too.
However, I'm always suspicious of those who think the Left needs to start waving the flag. That's entering an auction we cannot win. In the UK the Tories will always go at least one stage further than the Left is prepared to do. On the international stage the Chinese Fascists will always be more 'nationalistic' than Britain - even Tory Britain - could ever tolerate.
The answer, if there is one, is for the Left to be more knowledgeable about British history and to be more realistic about the history of other nations and other imperialisms. For example we are the nation of imperialism it is true. But we are the nation of anti-imperialism as well. Britain had a political culture that allowed room for critics of Empire as well as soldiers of Empire. That's not bad, when you think about other conquering powers in history. It's certainly not bad when you think of China now - a regime that cannot tolerate even the meekest of criticism from its people. A regime that locks up and executes dissidents, or sends them into exile. A State where there is only ONE version of history - a version that pours glory on the regime. Our little friend the Chinese Fascist - whether Chinese, Indian, or whatever he was - was doing precisely that (which is why I think he should have been given even more rope to hang himself). It was a revolting display of nationalism.
But when it comes to British or English patriotism, I'm all for 'show' not 'tell'. Don't wave the flag. Don't bellow the national anthem. Don't 'tell' people you're proud of your country. There's no need. Just behave like a broad-minded tolerant Brit, and insist your government does as well.