But when I only fuelled with £60, then £40 should be refunded
immediately. If it can come out immediately, it should be able to go
back in immediately. For example, if I'm in a shop and for some reason
they want to cancel the transaction (I've changed my mind or the
merchant typed in the wrong amount), surely it can be cancelled on the
spot, and all my credit is there for the next shop I walk into?
For some reason, that I have never really worked out, although it may
relate to the fact that, historically, at least, many transactions were
not pre-authorised, the transaction that actually debits the account can
take several days to go through the system. I think only when that goes
through is the authorisation removed.
In this context this would mean that, if they authorised the full £100
maximum, you would lose access to that full £100 for the best part of
the a week. If they only authorise £1, and do the main transaction
either unauthorised, or with a separate authorisation for the actual
amount, only £1 that you wouldn't otherwise spend would be tied up,
albeit it tied until the authorisation times out, rather than until the
payment is settled.
I suspect that reversing a transaction only affects the settlement
stage, and still leaves the authorisation on file.
In the days when cards were imprinted, the merchant would have to pay
for a phone call, to have a transaction authorised, so they would only
get authorisation if the amount was over the floor limit or the customer
looked shifty.