You may roll your eyes and maybe every electrician on you tube does suggest/do this.
But that doesn’t make it a good idea necessarily. The regs suggest as “recommendation” in a PME supply to provide an earth electrode < 20 ohm for a swimming pool supply. But do a risk assessment- are there any exposed conductive parts liable to be touched by the user of hot tub (likely to be class 2) ? Is it an overhead supply /rural installation ? What is the likelihood of a lost neutral in the supply ? In the event of the lost pen conductor is the bonding to water and gas in place and reliable ?
Weigh up pros/cons of using the DNO earth and bonding any extraneous conductive parts (Using 3 core SWA, marshalling terminal if required) and having a Ze of 0.2 Ohm, having protection by ADS fault protection and additional protection via an RCD ...or isolating this excellent earth , having a variable earth rod Ra of 100 ohms plus in most cases and relying solely on an RCD to achieve fault protection disconnection time in 0.4s. A rod and connection that could be damaged outdoors or disconnected. And some bright spark coming along and reconnecting the load CPC back to the pme at later date.
In summary - use the supplier earth that is excellent for 99.99% of the time or stick a brass spike in the ground and rely on an RCD for the off chance that the DNO lose the neutral only to your property while you are in the garden still wet and touching ...touching ...can’t think of what you would be that has a potential versus ground ?