If you want to shift your portfolio investments from a GIA to an ISA, please sell down your holdings in your GIA, then once you have opened an ISA portfolio, move the cash into that portfolio. Please read our article Can I transfer funds between my portfolios? to learn how to do that.
We currently offer in-species for ISA transfers, and will soon be releasing this feature to GIA accounts including internal portfolio transfers. Keep an eye out on our Community page for more updates on this.
Please note that ETF prices may move in the period you are out of the market. By selling and buying back, you will also be subject to the cost of the market spread. These factors may mean your cash buys back fewer shares than you held previously (equally, if prices fall while you are out of the market, you may be able to buy back more shares than you held previously).