I am thinking of transferring some shares from my 100% owned trading company to my partner. If there is a problem in the future, could these shares be transferred back without incurring any taxation, and can holdover relief (under TCGA 1992, s 165) be claimed on both the gift and the potentially returned gift? 

Arthur replies: 

It's not clear whether your 'partner' is your spouse or unmarried partner. Assuming it is your unmarried partner (because otherwise, you would not mention s 165 holdover relief), the short answer to your question is ‘yes’. S 165 holdover relief can be used when you transfer to your partner and when they transfer back to you in the future. See HMRC’s Capital Gains Manual at CG66880P.