We had the same thing last week.
Went out and found water rushing down the drive.
Appeared to come out where the sewer pipe came down the house. ££££'s sign at the thought of getting it sorted.
Then noticed it was still rushing down the drive, from a point outside the gate.
Water had pushed a telecom junction box lid off and water was pouring out.
The bit down the drive was coming out of their conduit, where they had brought the cable under the drive and up to the house.
Loads of stones and sand pushed out, water board were out in half an hour and fixed by 10.30 at night. Had to take our street light away as that was undermined.
As you say the amount of muck that gets pushed out is amazing. Lucky ours was a clean water main!!!
Hope they sort quickly and give generously for the replacement parts.