The case comes just after Picture Loans stopped running its ads because of "temporarily" suspending new lending amid the credit crunch.
Five people complained that the ad, which has aired for three years without complaints, implied taking out a loan was something to be taken lightly.
The ad, created by Watson Philips Norman, featured a couple at home -- the woman was filming the man while he was talking on the phone to Picture.
The man said to the Picture adviser: "We simply want everything in one place so we know what we're doing. Yes, we have a mortgage."
He then said to the woman "How much did we want to borrow, £25,000?"
Later he started to play with a football while on the phone.
Picture argued that the ad only showed someone making an initial enquiry rather than taking out a loan and it was apparent that the people took their financial arrangements seriously.
It also said even if a viewer seeing the ad could have been misled about any characteristic of the product, no substantial harm would result, because the paperwork sent to the customer which they would have to sign before the loan proceeded would soon disabuse them of any such misapprehension.
The ASA considered the ad was too light-hearted in tone and most viewers would have understood it to be about arranging a loan rather than making an initial enquiry.
The ASA also considered a single complaint about a different Picture Loans ad but did not uphold it.