Computing the amount to assess: business changes: one trade or more than one trade: carrying on a trade and a profession
It is possible for an individual to carry on at the same time both a trade and a profession (for example, the trade of editor and publisher and the profession of journalist, CIR v Maxse  12TC41). But, again, this is unlikely unless the two activities in effect amount to separate businesses (see the report of the Special Commissioners’ case of Salt v Fernandez  SPC135).
Where an individual carries on a single business activity (for example, an optician who tests sight and sells spectacles) that business cannot be separated into a part which is a trade and a part which is a profession. In such circumstances the business must either be a trade or a profession. It cannot be both. There are a number of Excess Profits Duty cases from the Second World War which deal with the issue - copies can be obtained from CTISA (Technical).
In the same way an individual can only carry on two separate professions if the activities are wholly unrelated.