Pebble dashing comprises of a sand and cement render applied over brick, block or stone etc walling. Pebbles are then pressed into wet render. Remove with a hammer & broad chisel. Consult with Planning department and also
check that pebble dashing is not concealing poor walling.
Most builders can carry out this work. Wall may need repair and repointing. Architects or Architectural Technicians can advise, see local yellow pages
Go to your local tool hire shop and hire a "Kango Hammer" ( A hand held electric tool a bit like an overgrown drill.) You'll need a Broad Chisel Point with it and probably a Voltage converter to 110V. Then find a nice spot, about chest height and work your way outwards. Pebble dashing will have 2 layers to tackle and it's a heavy beast to hold for a long time so try to let the Hammer do the work and use the weight to your advantage by working downwards where possilbe. Use Scaffold where required. You could get a builder but they will do the same thing and charge you a lot of money for it.
depending on the surface you may have quite a job on your hands, if you want to get back to face brick with no damage it is almost impossible (almost). if the dashing is fairly loose you can sometimes scrape it off with a steel bladed floor scraper, or you could just take off all the loose then go over it with a new dash or flat render. online render and pebbledashing tutorial http://www.goldtrowel.org