I have noticed that my 16 month old bitch has blood in her faeces this week. She is eating ok but seems to have slightly less energy than normal. I just thought this was because the weather is getting warmer. She is also a bit more "clingy", otherwise she looks very healthy. She is wormed regulary. Does anyone have any advise? Should I be worried or take her to the vets?

I'd definitely take her to the vets if she was my dog.  Hope she improves soon.

what food is she on??

Is the poo normal consistency otherwise, or soft / slimy? I would take her to the vets to be on the safe side. :-)

She is on James Well Beloved & Nature Diet. She seems to have picked up now, is less clingy & there appears to be no blood now. Will keep a close eye on her.

Good to hear your girl seems better. I would still take her to the vet for a checkup, though. No visible blood doesn't always mean no blood at all. A simple blood test will tell if something is going on, making her slowly seeping blood somewhere in her digestive system, or will show she is allright :-) 
It's such a small thing to do, to be on the safe side :-p
Karen