Why do so many shopping trolleys find their way into the canal?

Surely a single glance would rule them out as potential waterborne craft - the wheels being the biggest clue that, as transportation devices, they are best suited to terra firma.

British Waterways may think they have a problem with discarded shopping trolleys, but in the world of e-commerce abandonment of shopping devices is rife. Nearly fifty per cent of all on-line shoppers never make it to the checkout in what is known as 'the basket abandonment problem'.

How exactly do you liberate a trolley from the supermarket that owns it, anyway? Presumably they are all corralled up at night with a shepherd to watch over them, so you must have to trundle them out of the car park and down the road in broad daylight with a "this is perfectly normal" look on your face.

But few supermarket shoppers will abandon their trolley inside the store. There would have to be a pretty big queue at the tills before you'd consider it wasn't worth waiting to secure the items you had spent the last half an hour choosing.

Most of us also enter stores knowing that payment will be required at some stage if we are to obtain any goods.

It's therefore unlikely that on-line shoppers get surprised when asked for their card details and abandon their baskets in dismay. No, the basket abandonment problem is partly down to poor usability.

If on-line shoppers get confused, annoyed or irritated by your checkout process, because they can't select the quantities, colours or sizes they want, they will simply walk.

If it is not crystal clear what they are about to purchase, and how much they are going to pay for their goods - including shipping and tax - they will not proceed.

But usability is only part of the picture. Trust is also a big factor. Repeat customers have a much lower basket abandonment ratio.

They have already worked out how to use your on-line store, they have previously accepted your terms and conditions and hopefully received exactly what they thought they had ordered.

The old adage, that it is harder to get a new customer than keep an existing one, is true on-line too.

Few site owners are aware of their basket abandonment ratio. A good shopping basket system will be able to generate such a number, along with a gold mine of other product sales statistics.

If your site has a basket abandonment figure of 60 per cent or greater it's time to call a usability expert.

If it is down round the ten per cent mark you've clearly got something right - or your prices are way too low!

Chris Tomlinson is managing director of Internet consultancy WebXpress.