I adore labs .... but can't decide whether one is for me or not - must get on with my cavi (who is gorgeous, but little and sweet).  Please any advice please on what they are really like.  Many thanks.

The best advice is to spend some time with some.  It is hard to describe with words what a dog breed is like.  What one person means by "playful" another person might think of as "chilled".

I'd advise you to look up some lab breeders or owners in your area and explain that you are thinking of getting a lab, and could you come along and spend some time with them.  Alternatively, get in touch with your local gundog club and ask if you can go and watch a training session - there should be labs of all ages there.

With all due respect, a lot of us have already explained more than once the dangers you would face if you left a Labrador puppy/youngster alone all day with your Cavalier. It might be a better idea to consider either a different breed, or an older (say 4 plus) rescue Lab that is calmer than a pup.