Hot Tub Electrics

Would more likely be better to take designated power down to the hot tub area

Hot tub extension leads like those from Tough Leads are generally only suitable for temporary use and are not recommended for running a hot tub 24/7, as the continuous high power draw from the heater and pump can cause overheating and increased risk over time, even if the unit has an inline RCD; the safest and most reliable solution is to have a qualified electrician install a dedicated outdoor supply, such as a weatherproof socket or armoured cable, which is specifically designed to handle continuous use and outdoor conditions.

This should be fine in theory though I would have reservations about it for a couple of reasons. Though this cable is tough and UV resistant if you are going to use it regularly at the back of the garden then a fixed properly installed cable would be better in my opinion. The other issue is the Hot Tub according to the instructions has a 10mA RCD on the plug so if you are plugging this in to a non RCD protected socket located inside the house then all is fine but if you plug in the extension cable to a non RCD protected socket the lead will have no RCD protection! An 8 year new build should have RCD protection but this must be checked. Also the RCD protection will be 30mA to the Lead (if it is installed) so if you do this make sure the extension lead is no where near the hot tub. The socket needs to be 2m away from the tub but the extension cable must not run near the hot tub. It sounds like the hot tub plug has an RCD built in so make sure you get the cable with the box that allows that to fit if you do do this. Also check that you don't have a split board with AC type RCDS and any solar, ev charging or battery storage. 8 years old would make it highly likely it is a split board with Type AC RCDs and whilst that is perfectly fine any heavy electronic equipment with DC can blind those. One further issue to consider is Volt Drop you don't state the length of your garden, the hot tub already has a long lead so any additional cable will result in a volt drop if the length is excessive this could become a problem. Hope that helps.

Personally I wouldn't trust any extension lead as its another point of failure I always recommend fitting hot tubs on its own circuit