Section 104 shares in an ISA

When calculating the average cost of shares in a section 104 holding, for CGT purposes, should any shares that have been transferred into an ISA be included in the calculation? Or can the shares in the ISA be completely disregarded? In other other words should the average price/cost base only be based on the shares outside of the ISA?

Hi
These can be disregarded as ISA's are tax free.
You also cannot claim any losses in respect of shares held here.

Would it also be correct to assume that shares held in a sipp are not included in a section 104 holding as well.

Hi,
Shares held in a Self Invested Personal Pension (SIPP) are chargeable to Capital Gains Tax.  They can be included in a S104 holding. You can see guidance here: Shares and Capital Gains Tax (Self Assessment helpsheet HS284)
Thank you.