I have just extended my kitchen so that the rear egress is now through the dining room. The local authority safety officer has insisted that for full safety approval we should install a sprinkler system in the dining room. This would involve digging up the road outside and running new piping into the house. The water company has advised me to seek an indepedent assessment as they say this is absurd for a small private residence. I live in West Sussex. The man from the local water company said he'd never heard before of a private residence in that area having to install sprinklers

I googled and found THIS

I cannot be definitive without plans or a full survey of the layout of the premises however there are situations where sprinklers could be required as a compensatory factor in a dwelling house but I do not believe this is one of them, providing the dining room leads into a hall that has an exit to outside the building or the dining room has an exit to outside the premises. This is an inner room situation and the kitchen is the inner room which is acceptable in Approve Document B (fire safety) Volume 1. You may be required to have interlinked heat detector in the kitchen and smoke detectors in the hall and/or dining room to give you early warning of a fire in the dining room or hall.

Check out ADB pages 15 & 18 for a start then discuss it with the building control officer and if necessary contact building control.