I would just love to hear your argument for leaving a TN-S earth behind, in favour of a crap UK TT Ra value??
I'm not getting into the PME argument here, but i sorely disbelief you've seen a full broken neutral, if you have you are amongst the very few that have!! I have a very good friend that has just retired from your area's DNO, he's been with them and the old Regional leccy boards since leaving school, and retired as a Regional Manager. .....He has only known of 3 such instances in all that time, all were tripped out by there protection relays...
As for the ''hot tub'' senerio, you make allowances/provisions in your earthing arrangements when this is a factor in your installation. The truth is here though, how many hot tubs have you seen in the back yards of housing estates, ...not many i would think. Common as muck mind in Cyprus among the Brits...lol!! Now think about it, ..what do you think would be needed if a house owner foolishly locates a hot tub on his lawn, and not on a substantial base, patio, or Decking??
One last thing, in certain parts of Essex, i would agree with you, using a rod, because in those area's that i know of, i know that i can get better than a TN-S earth, with a couple of rods coupled together. lol!!! Yes, i know Essex very well!! lol!!