Gas supply to house installation

[hi1]

Having brought an old housing association property without a gas supply into the house i'm trying to get my ducks in a row for job priority list.
I will have to dig a trench minimum 375mm deep up front garden from council footpath, 14 meters long. to front of house and meter box. Running across the proposed trench are a foul water/blackwater drains about 110mm diameter in i hope clay and not pitch fibre. There are 4 houses connected to this run of pipe. Its chamber is 7 bricks deep with a steel cover so about 2.5 feet deep. My question's are
1. Can the pipes actually cross over one another?
2. If so can the gas go over the top or underneath as a preference or requirement?
I believe if i dig the trench myself it has to have slotted ducting laid with a rope through to enable the utilities people to pull through the actual supply pipe. Other than it being to short is there any reason i can't install my own 32mm pipe in the duct?
Having spoken to the ultilities they seem quite happy to dig a trench on my ground at vast cost and lay the supply pipe directly in it with no ducting. Why do i have to duct if they don't?
Thanks for any advice. If it's the wrong forum there doesn't seem to be one for this.

 

[oldbutnotdead]

Can't help you on the gas supply regs I'm afraid. Generally with utilities it's their ball- ducting is cheap enough, if that's their spec then jfdi. I'd advise under that soil/waste pipe and don't dig all around it- spade either side (so there's a bridge of soil under the pipe then poke a hole through the bridge when you're at depth. While you're digging trenches, how's the water supply pipe to the place? - if it's lead or steel now would be a good time to update it.

 

[mrrusty]

When we had a new gas supply installed about 4 years ago - approx 15m- they moled it between 3 holes. It didn't cost much either <£500 (but the main was in our private track not the street)