> I just discovered that 'marvelous' has an accepted alternate spelling. John LeCarre uses 'marvellous' A LOT (nothing like
an unexpected spelling to make a word stand out). Is this yet another British anomaly?

To tell you the truth, I had never heard of the first spelling!!! Marvellous has always been the way that I have spelled it. Conversely, I can ask - is 'marvelous' an American anomaly?!