I can't see anything in Halsbury's about the use of alias - it was possibly just common usage as to which way around the names were used in IoM wills.There is no legal requirement to use one surname rather than another. In British law, if I read it correctly, people can call themselves anything they like, so long as the intention is not to deceive. Most countries require you to legally register a change of forename, but to use a different surname you just need to be known by that name.
Sue