I thought of that.
I checked download rates from London, Maidenhead, San Francisco, Los Angeles, and New York, all checked-out at 4Mb which is normal for my local node. In fact the London and San Francisco links are usually slower, so no problems there.
No browser issues either.
I checked the Amazon S3 logs too, they showed no errors, so it looks like a problem with an intermediate routing node 'near' the S3 servers, possibly just sheer bandwidth oveload.
It seems to have cleared up now, but it's a little worrying as los of images in the last few hours of an auction can mean no bidding during the final phase so items may be sold for starting price only.
Last night I had a lens sell at a £22 starting price which is of a type normally selling for twice that. Could be just be a normal fluctuation in buying patterns, but loss of pictures would have certainly turned away anyone else interested in the item.