I didn’t think you could. Once you have acquired 20% of a company you are obliged to disclose your intentions. You don’t have to launch a takeover bid, but if you say you don’t want to and sit there then you are only allowed to creep your holding up by 3% every 6 months. Your bid doesn’t have to be for all the shares - you might say you only want to acquire say 55% which of course gives you a controlling interest without having to spend the money, but generally when they launch a bid then it’s for all the shares. Compulsory acquisition happens when they have received acceptances for 90%.