CTM40965 - Particular Trades: mutual concerns: non-mutual transactions
If a body has customers who are not entitled to receive back surplus amounts they have contributed to the common fund, its transactions with them are not mutual. Tax has to be paid on them in the usual way as trading income. If the amount of trade that is not mutual is very small it will not affect the tax treatment of the mutual trading.
Bodies may have dealings, some of which are trading and some not trading. Decide whether the dealings are trading transactions before deciding whether the trade is mutual. This distinction is covered in BIM24010.