So, there was an article in The Times yeterday about the many and varied suggestions that had been put forward for this in response to some survey or other.
Matthew Parris came up with:
1) World War One
2) The failure of the Irish Home Rule Bill
3) The Boer War
That sounds pretty plausible to me although I would be tempted to replace the Boer War with appeasement of Hitler culminating in the Second World War, however, in contrast to World War One that conflict was definitely a global phenomenon so I'm not sure whether we should classify that as a British mistake.
What do YOU think were 3 most inglorious moments in Britih history?
NB: The birth of June Sarpong cannot be used more than once.