Does this mean that TT installations will again need an RCD before
the CU?

No.
(They never did, although that was the cheapest option before having a
single RCD protecting all circuits was explicitly called out as non-
conforming.)

Thanks but I am not clear that addresses the point I had in mind. The
ESC Q&A on this:

Question
"Is an RCD main switch (such as a 100 mA time-delayed device) still
required in the consumer unit of a new domestic installation forming
part of a TT system?"

Answer
"For a domestic installation complying with the 17th Edition where all
the final circuits are RCD-protected, an RCD main switch is no longer
required, provided that the consumer unit is of all insulated
construction."

I wondered if the new fireproof CUs were likely in practice to be "all
insulated
construction".

--
Robin
reply to address is (meant to be) valid