When i bought my home in the UK six years ago, i phoned my bank, told them how much i wanted to send and to who, and they did it, with the money arriving straight away. If the amount had been less than 20k, i could have done it online rather than over the phone; the back-end payment machinery is the same, but i suppose the bank think there's less chance of a normal customer making a mistake with a large transfer if someone walks them through it. My bank is rather old-fashioned; more modern banks let you make large transfers online or through their app:
https://www.starlingbank.com/blog/high-value-payments/
That page mentions that "one of our team members may need to double check a few details before the payment can be made" - again, that's nothing to do with the machinery, that's in case you match some pattern looking for fraud or money laundering etc.