Found at local car boot sale this week, I think its a farriers tool of some sort.

Looks like an early attempt at a vise grip wrench.  :-)

Looks like some sort of a spring compresser.  Not for engine valves with the bulkiness, but something that would be repetitive once set up. 

Yes, farriers could use this to put caulks onto horseshoes, before installing on the hoof.  Great because of the repetitive capability.  There is another vise, sometimes called a caulking vise that was much heavier, and foot operated.

I am with John K on this one.  Is there a name on it?  It might have been made by Champion Tool Co. (the predecessor to Champion DeArment, which then became Channellock).

Sorry no name at the moment, I will clean it up and let you know. What are caulks ?

I absolutely retract my spring compressor guess.  Calk installers!  Somewhere I have a wrench from Diamond (Calk, Horseshoe, Tool) Co. Calks were used to increase traction like tire studs or chains.  The calks are the inserts in the horseshoe.       

FROM ALLOY ARTIFACTS:
   http://alloy-artifacts.org/Photos/tools/diamond_oe18_wrench_calk_f_cropped_inset.jpg

Caulks, right.  In the horse drawn days, they were absolutely necessary for traction on ice or frozen ground.  If your work horse fell pulling a load, could break something and be put down.  Which could put you out of business.

So , some of the calks are pressed in? The ones I have here are threaded. The wrench is marked Neverslip, but does not fit the calks here. I have always yhought of it as a Calk Wrench, but I have been wrong before!!

Great help thanks for your answer

Calks also get used on loggers boots (or used to, haven't gone there in a while)...   rumor is that it caused all kinds of trouble in bars as the calks tore up the floor (kind of like the old metal ones in tires tearing up pavement).

lptools, your "Neverslip" wrench is indeed a calk wrench.

Neverslip / Neverslip Mfg. Co / Neverslip Works, Hamilton & Neilson St., New Brunswick, NJ / patent 588438 Aug 17 1897 J.W. Johnson & R. Whitaker / http://vintagemachinery.org/mfgIndex/detail.aspx?id=10699 / https://wrenchwiki.com/neverslip-manufacturing-company/ / https://www.datamp.org//patents/displayPatent.php?pn=588438&id=22132

Thanks for the info!!!

Shoot, guys, I never would have pegged the OP's tool as a farriers tool. 

Quote from: john kIn the horse drawn days, they were absolutely necessary for traction on ice or frozen ground.

In the big cities of the day  - New York, Boston, Philadelphia - the number of horse-drawn vehicles would have been enormous. Every one of those horses had caulks affixed to their shoes in winter weather.
Poring through old catalogs and trade journals, one will find hundreds of advertisements for horseshoes, horse nails, caulks, and devices for attaching them. It was big business.
The shops that tended to the horses were the tire shops of the day. Kind of hard to get your head wrapped around it in the current era.