According to some embittered nations, we the British (and worst of all the English amongst us) aren't allowed to feel any pride in our nation, ever. This is because we must personally carry some sort of burden of shame for some historical events which were admittedly not our finest hour.
The truth is that most British people who are patriotic, feel that way because of recent historical events that have occurred after the second world war. The formation of the welfare state, the National Health Service, innovations and inventions in technology and industry, British music and arts, the multi cultural aspect of British society which has in the main been successful and so on. We're by no means perfect but we're not a bad bunch either.