I have a 6mth labrador puppy and am receiving conflicting advice about exercise levels.  He is from field trial pedigree so is a fairly slim build and not as big as some other pups we meet.  he gets about 20-30 minutes free walking (running!!) on the beach or common and another 20-30 minutes road walk on a leash each day.  is this appropriate??  he always seems keen for more, but i am worried about damaging his hips

Hi,
A general rule of thumb is that a pup (and this includes working labradors!) should have 5 minutes exercise for each month of age, per walk. So a 6 month pup should have walks of no more than half an hour. And most of this should be lead work and training rather than tearing about freely. So your pup seems to be getting about the right amount.
:)

Personally, I don't mean to be nasty, but I would have thought that that amount of free running (20-30) plu 30 minute road walking, at that age was a just a little bit too much. I don't own Labs, I have Beardies, who love free running, but at that age, I wouldn't let them do that much DAILY, as they also run about in the house, garden etc. At that age, mine get about 10 mins, mainly so I can teach them to come back, get used to being off lead etc. They would also get a 20  minute walk twice a day, to slowly build up muscle. Every owner will probably have different advice for you though, depending on their own experiences.  hope this helps!
Kay