No.
Someone on 40k would be taxed 20% on their income over ~£5000, so ~£7k per year.
Someone on 70k would be taxed 20% on their income from ~5K to ~41k, then 40% on their income from 41k to 70k. So total annual tax of roughly 7.2+11.6=18.8k.
So, 70k guy takes home 18.2k more than 40k guy.
thanks, I thought the 40% tax was on all your earnings.