The point of an up front S type is back up should the 30ma RCD protection fail, RCD's apparently being of questionable quality these days and without a functioning RCD a typical TT will have zilch earth fault protection. There is good reason to include an S type then, but it is not a requirement, and the point could have been much better made by bigspark.
Personally I have not carried out a TT for a while,and most that I do are temporary installs regularly tested and inspected. For those I am content to apply regulations only as I don't find 30ma RCD's nearly as unreliable as others suggest. If I was carrying out a permanent TT install which would be unlikely to be re-tested for years,if at all, I would definitely include an S type up front.