Oh, man, this is a good point. The rules don’t specify which ATM to use; as I understand it, the person setting me up is just keeping an account stocked with money sufficient that an ATM connected to the network will always have enough money in it.
So I’m designing my own ATM.
It accepts my card, but no other. It has an express slot, where you swipe the card and put in your code, and it spits out five bucks (I know the OP says pounds, but I’ll take it in US dollars just to avoid the inconvenience of trying to type that weird little L symbol). I bet that we can get the whole process down to to 20 seconds, most of which is taken up by communication with the bank.
I bet I can have that ATM designed for less than a quarter million bucks, but let’s set it at $250,000.
Step 2: a robot. For $10,000, I’m pretty sure I can hire some engineering grad student to design a simple robot that swipes the card and types in the PIN and snags the fiver and puts it in a stack. Let’s figure the robot is crazy energy inefficient, uses $5 of electricity a day. The ATM uses another $45 a day in electricity–super inefficient!
Step 3: someone to refill the ATM. How much can it cost to keep the ATM in fives? Let’s be super generous and pay a company $550 a day to keep it stocked and to guard it (maybe I’m renting a closet in a bank).
At 3 transactions a minute, that’s $15 * 60, or $900 an hour. The daily haul is $21,600. Minus costs, that’s $21,000 a day.
Startup costs are paid in two weeks. After those two weeks, I’m earning $7,665,000 a year.
I may decide after the first few months to use a couple million of my earnings to buy myself a nice house and move the whole operation into the house.