in my professional opinion this will definitely not open up with a hammer and chisel. There are not any localities wher eyou can take a hammer and chisel to a pebble and it opens up fantastic. Lyme regis, whitby amd isle of skye are the ones where this does occur.
The ammonite looks like some kind of Schlothemia type ammonite .. in fact it looks like Schlothemia angulata. Ammonites from that coastline are not uncommon but good ones most certainly are. As a professional preparator i would suspect that this will not turn out too good even with air tools, but it will certainly look better than it does now.
I am sure there are professional preparators other than the ones mentioned above in the lyme Regis area that could also tackle your ammonite.
I sadly can not as i no longer take on other peoples prep work. :-(