tax on capital gains, page-60

You can use any strategy you want, as long as you have written evidence of what you have done to get to your figures.

If you bought 3 parcels 50k, 40k, 60k and you sold 20k. If you can show you sold 10k of the 50 and 5k in each of the 40 and 60 it is all legit.

Obviously you can only claim your brokerage once in the transaction as part of your cost base though. It is easier to use the full brokerage in the first transaction, rather than splitting it up over multiple sells.