Ive been asked to run a mains feed to feed a tea cabin in a courtyard behind a shop. Its on land being leased from the shop which has the mains water supply. They want me to tee into their supply underground and run the new pipe to the new tea cabin. It will involve digging a trench across a 3m wide right of way tarmac access road to a house, packed gravel and soil either side. The existing mains supply is about 450 deep. What would be the minimum allowable depth for my supply trench for this purpose. Im thinking the trench only needs to be wide enough to pick down to a suitable depth. If I dug a trench just wide enough to get the pipework down 200mm? Please help, im not sure where to begin.