How do you spend a penny in Stockholm's cashless society?

You wouldn't think Bjorn Ulvaeus had any cash problems - as a member of the seventies super group Abba he made vast piles of it. He even wrote the hit Money, Money, Money.

When I met him in Stockholm I had the odd sensation that I already knew him - his face is so well known.

It wasn't his public persona that he was talking to me about - it was his personal beliefs stemming from a family incident. After his son was robbed he decided we would all be better off without cash.

I was amazed by his energy and boyish enthusiasm for the cashless society. He thinks it makes crime less likely because robbers wouldn't find much of it in our homes if we use more cards.

He also thinks that it cuts costs by reducing the expense of counting and guarding money.

He has lived without carrying cash for years and feels so confident of his views that he asked me to pass on a public challenge; if anyone can come up with a convincing argument against going cashless send it in.

If you feel you have the right argument, email it to yourstory@itv.com.

I am less enthusiastic about going cashless than Bjorn. Getting us to desert our notes is really good for companies, because it allows them to cut the overheads associated with cash.

It's also good for the banks and technology firms, which are busy forming new and powerful alliances to push us further into the realm of the "digital wallet".

For consumers, though, it surely brings privacy issues. Every transaction through our cards leaves an audit trail.

It also opens us up to new forms of identity fraud, something that is vastly increasing in the UK, Sweden and around the world.

Often though the weak point of a seemingly powerful argument is more simple than we first suspect.

"Surely", I asked Bjorn, "There have been times when you wish you had cash on you".

As his face crumpled in a slightly embarrassed smile he replied, "In Stockholm many of the public toilets need a coin and I have been caught out before, now I do carry one just in case".

Watch Chris Choi's full report from Sweden tonight on ITV's On Assignment at 10.40pm.