Is trading the same coin for gains taxable?

As the title says, I’ve had a read of the crypto tax for the UK and understand that trading from one crypto to another is taxable (gains), but what if say I was in Jasmy and I sold high, buy back in the same day low, so gain more coins for the same amount of money, you get it.

Are these trades taxable? I’ve been doing this for about a week now to fill my bag basically free of charge (albeit a lot of high risk). I thought once I actually withdrew so the fiat hits my bank, then that is what I’ll pay tax on, otherwise I’d be getting taxed twice over?