This is actually an interesting question:
We have previously postulated that banks can only charge interest on the actual balance in an account. This was assumed to be the reason why pending but not collected card payments aren’t included in your balance for the purpose of calculating overdraft fees.
If pots are just ring fencing money in my account, without actually taking it out of my account, then at first glance that’d appear to be similar to the ring fencing done for “pending transactions”, and by the same logic one would assume that it would be against the law to charge for an overdraft if I have -£100 in my main account, but +£200 in a pot, as my total balance would still be positive.
Clearly, Monzo doesn’t think so. So were did I go wrong? Does anyone have theories?