I live in the UK but am due to personally receive a one-off payment of millions of dollars - representing the majority of my personal wealth - from a US-based organisation with whom I do business. The organisation has the money in dollars and has no UK presence nor UK bank accounts, but I would ultimately like to have it in GBP, since I intend to continue living in the UK. The means of payment are negotiable and both parties would like to avoid getting screwed on currency exchange fees.
It is well-documented online that doing an international wire transfer from an ordinary US bank account will result in receiving an unfavourable exchange rate plus fees, and sure enough this has occurred when I have had US-based organisations pay me via wire transfer to my GBP account in the past. However, when I have previously tried instead having organisations pay USD into a personal account I created with a currency transfer service like Currencies Direct, and then from there paying it out as GBP to my UK account, I found that even for six-figure transfers, the exchange rate available was still around 0.7% worse than the "interbank rate" (looked up via Google) at the moment of the transfer - despite currency transfer services like this marketing themselves as a better way to perform such transfers! For my 7-figure transaction, this 0.7% cut will represent a loss of tens of thousands of dollars to financial middlemen, which I would naturally like to avoid.
What can a person with lots of currency to convert but no special connections to financial institutions do to convert currency at a rate closer to the interbank rate? I can find a few services that advertise that they provide currency transfers at the interbank rate, like Revolut, but in all cases there are strict limits on how much money can be transferred and the services are not intended for large transfers like mine. Is eating a ~0.7% loss on every transfer like this just an unavoidable cost of doing business across countries and currencies, or is there some trick that I'm unaware of that other millionaires use when they need to convert their money between currencies - such as buying some liquid asset on some kind of exchange for dollars and then selling it for pounds?