For long while it has been normal practice for the house earth to be based on the cable sheath rather than water pipes.
Eh? Yes, it has been a long time since water pipes were allowed to be used as an earth electrode as part of a TT supply, but a TN-S supply (using cable sheath as earth) is not the only arrangement currently in common use around the country. The majority of new installations will be TN-C-S, which uses a combined protective Earth/Neutral connection at the cutout.
The existing cable and clamp may just be protective bonding, rather than providing the main earth for the house. Obviously, this needs to be checked by an electrician to make sure you're not left without an earth after removal of the old pipe!
Assuming you have a cable sheath connection then thats not a problem although it would be considered better by many to earth metal water pipes inside the property. Only the gas pipe HAS to be earthed.
Incoming water and gas mains must both be bonded. This can only be avoided if all, or the vast majority of, the pipework is plastic. Even if the incoming supply is MDPE, the water supply must still be bonded at the stopcock if it converts to copper.