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Thanks for the reply. Not sure if I'm misreadng/misunderstanding you. Say for example I pay £200 into a broker account. Forgetting fees, let's say I buy £100 of crypto. So I then have £100 remaining in my broker fiat account and £100 in my crypto broker wallet. Do the brokers not allow you to hold the public and private keys for the crypto investments you've made via them? Apologies if I'm not understanding, however my preference is to hold my keys in my own offline wallet and for the broker not to have the private key. Is this not possible?
When you say the world deposit means then there will be no control over the fees. The platform will allows you to withdraw at any time you want but they are going to release not by yourself. You can use peer to peer platforms which are completely decentralized but you cannot deposit any amount, you directly pay the seller's bank account and will receive cryptos once the payment was confirmed by the seller and escrow.