I have been looking at this too. From my understanding re-buying the same asset within 30 days is not allowed and it needs to be different. Exactly how different is one to question and probably hard to get an answer for.
I believe i have a good solution for anybody who has a cash ISA that means you are not out of the market for 30 days. Its what i am thinking of doing:
1) Sell Index funds in Taxable account realising less than £12k profit (get as close as possible)
2) At exactly the same time use my Cash ISA to buy the same funds into my stocks and shares ISA account
3) wait 31 days
4) Sell Index funds in stocks and shares ISA account and put that cash back into my Cash iSA
5) At exactly the same time buy Index funds in Taxable account with money released in step 1
As long as you don't have transaction costs i believe this should realise the profit, allow you stay in the same funds and also ensure you are not out of the market for the 30 days the tax man wants if doing this purely in a taxable account.
I think this would stay within the rules, but if anybody thinks differently it would be good to know