Boffo,
"1 - that UK will require ever decreasing numbers of DD/FF, because 2 - shipbuilding costs will rise inexorably."
No figures for the future fleet are available, but I'm guessing it'll be twenty escorts, six or eight T45's plus T23 replacements. I don't see why costs should rise- DIS states that we maintain a "core" capability, but also that the UK should shop abroad for the low value steel bashing where appropriate- the complex high tech stuff being done back here. However, if "Shipco" comes to pass- and this enterprise can rival its foreign competitors, we may find that steel bashing becomes more competitive here in the UK as Shipco wins export orders needed to drive down unit costs?
"the next DD/FF design will be 2025 (just in time to forget everything learned for FSC)."
That would surprise me. Planning for T23 replacement needs to start NOW. With the CVF's out of the way we'd need new escort construction to begin strait away.