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HMRC internal manual

Business Income Manual

Computing the amount to assess: business changes: one trade or more than one trade: losses

S45 Corporation Tax Act 2010, S83 Income Tax Act 2007 

If, as a matter of fact, a company carries on two separate trades, and one of those trades ceases, any losses arising in that trade may not be carried forward and set off against the profits of the remaining trade. See BIM80565. The same principle applies to individuals. See BIM85060.