CG57700 | Unit trusts: different portfolios
From HM Revenue & Customs · Capital Gains Manual
If a unit trust has a number of different portfolios, transfers by a unit holder between each portfolio should be treated as a chargeable disposal and an acquisition of new units. TCGA92/S102 prevents the share reorganisation provisions of TCGA92/S127-TCGA92/S131 from applying to the transfer.