Computing the amount to assess: business changes: one trade or more than one trade: general principles
There is nothing in law to prevent the proprietors of a business, whether unincorporated or incorporated, carrying on more than one trade at the same time (although in the case of farming, S9 Income (Trading and Other Income) Act 2005 provides that all farming carried on by any particular person shall be treated as one trade, see BIM55115). But in the case of an unincorporated business it is unusual for business activities carried on by the same person or body of persons to amount to more than one trade unless
- the two activities are so fundamentally different that they cannot constitute one trade, or
- the activities are not interconnected, interlaced nor interdependent (Scales v George Thompson & Co Ltd  13TC83).