Seems to have spiders all over it too, which i keep taking off :(
Its a hanging basket variety ..something millions.
(http://i35.photobucket.com/albums/d173/springbokgirlie/DSC00043.jpg)
Looks as if it needs feeding to me. Or doesn't like the cold. As it's in a basket (and not protected by other plants), it's probably in a draught.
I think it just needs a bit of a cosset.
Yes the stem seems healthy, maybe it's a bit too exposed? And in a pot yes it will need lots of mucky stuff to help it grow ;-)
I find though that tomatoes tend to lose their bottom leaves quite often. When I see yellowish or manky looking leaves, I chop 'em off straight away.
It looks OK apart from the bottom leaves, so take them off, give it a feed, and see how it does.
Chop the yellowing leaf and I'm pretty sure anything with 'million' in its name (Sweet Million) is a cordon/indeterminate not a bush so also take out the side shoot that seems to be coming up from the base.
It's not a huge pot for for the type of tomato so you'll need to water/feed very regularly - perhaps a heavily diluted feed each time you water would be best rather than a weekly feed.
SBK - I think this one of a few different varieties I sent you for container growing?.
I have both the sweet million and sweet olive in 12" pots which are doing okay and tumbling tom plus gartenperle in hanging baskets.
I agree with the advice given - when growing in pots you will need to feed and water regularly as they are heavy feeders/drinkers. You will also need to make sure that you keep the compost as erratic watering (letting the compost dry out and then saturate) will cause problems when the fruit appear.