Below is a portion of a photo that appeared in today’s New York Times, taken at the Westminster Kennel Club Dog Show, in New York.
My eye was immediately drawn to the sign saying “DOGS ON LEAD ONLY.” I only became aware of the expression “on lead” during a trip to England two years ago, when I encountered it as the equivalent to what Americans would call “on a leash.” My guess is that it’s been used in American dog circles for a long time; I’m sure readers can fill me in on that score.
notoneoffbritishisms.com 
We don’t use LEASH
I believe this is just an example of the omission of prepositions that is commonly used in instructions, such as ‘insert cup before selecting drink’. I have never heard anyone use something like “I always keep my dog on lead” in speech. I think British people would be more likely to say “…on a lead”. Perhaps there are some dog aficionados on NOOBS who know otherwise.
Or “on the lead”. I have seen “on the leash” in the UK but it’s usually in by-laws or official notices (“Please keep your dog on a leash”, for example).
That’s exactly what I thought. “On lead” isn’t a recognised or established phrase, as far as I know. I’m not into doggy circles or shows, though. Dogs being walked around here are on leads.
Just to clarify, I have never heard either “on lead” or “on a lead” in the U.S.
Having recently adopted a new puppy, our family has been watching helpful training videos online. I couldn’t help but notice all the trainers (Americans) kept saying “on leash,” as in, “Keep them on leash when going for walks.” But of course normal people would say “on a leash.” So maybe the “on ____” combination is a dog training thing, and British English uses “lead” instead of “leash”? Just a guess. I know when my kids play Minecraft, the rope you put on an animal’s next is called a “lead,” not a “leash.” That was the first I’d heard it, a couple of years ago.
Maybe this is only for dogs from Flint Michigan.
Jon: Ooof.
Am I missing some American humor here?
Arthur, the city of Flint, Michigan, has had a health crisis because of lead (the mineral) in its water.
Leash was in common use in the UK (Midlothian) when I was a kid, it was the preferred term from what I remember but my other half (Kent) finds my use of it odd so it may be there is regional variation in the leash/lead use in the UK.
My Scottish wife’s father used the term “leash” years ago (in Scotland.)
When I met him first he used to take his family on caravan holidays and I remember the caravan sites having signs saying “dogs must be on leads.” Since then I don’t recall “leash” being used. I suppose leash to be an obsolescent term in the UK.
Also, do North Americans use the expression “Lead rein” in horse circles?
“I suppose leash to be an obsolescent term in the UK.”
I believe this is another case of the AE usage surviving the BE one. The word “leash” came into English in the 13th Century from French “laisse” – long before AE was even around of course.
So in BE, it looks likes a case of “lead” eventually usurping “leash”.
By the way, in French, whether you’re walking your dog through the Parc Mont-Royal in Montréal or along the Avenue Kléber in Paris, you’re using “une laisse”.
Leash was in use when I was a kid (NW England)/ There’s also “unleash” but I’ve never heard of “unlead”.
Maybe it’s been changed because “leash” implies something that’s restraining a vicious predator and “lead” implies something that’s guiding a well behaved animal?
The Brit horse expression is “on a leading rein” in my limited experience.
You can lead a horse to water
but a pencil must be lead.
Stan Laurel