I just received a HTML newsletter from play.com and it reminded me of something we discovered with Gmail a few months ago...
Since the powers-that-be at Google created a new class of font-size:80%, horizontal spaces have been appearing between images. And it looks like play have unfortunately (maybe) fallen foul of it.
To fix it, simply adding font-size:0 to any <td> tags containing image.
Eg. <td style="font-size:0;">
It is possible that this will cause spam software to wonder what you're up to, but on the whole it seems forgiveable.