If what
@timmymagic says of the state of British munitions & ordinance is any guide . . . (see below),
Small arms production....gone
Tank factories....gone
Artillery Propellant production....gone...now a housing estate...
War reserve shell production....gone
Large calibre barrel manufacturing....gone
then the UK seems left with little choice--in the short term--for many weapons systems requirements. Buy foreign to grow the force, with possibilities for license production, while
rebuilding over the long term the defense industrial base.
It's amazing that the seemingly mighty USA, while--of course--having a much greater indigenous production capability than the UK, is still hobbled by the contraction of our domestic ship-building industry. There was an excellent Wall Street Journal article on the subject a few weeks ago.
The US, the UK--really all of the Western states that had truly independent defense industrial bases (DIBs), an enormous amount of capacity was eliminated post-Cold War and its frankly never coming back. The "peace dividend" co-occurred with the overall deep de-industrialization of the 1990s.
Actually, had the Cold War not ended--let's say Gorbachev is successfully ousted in a coup--it's an interesting alt-history question of whether the closure of so much manufacturing capability would have occurred at all! Or at least on the same scale.
I realize the discussion topic is on the British defense industry in particular, but my point is Britain's situation is not unique.
Or, perhaps more specifically, if the UK permanently loses most of its DIB it will be in the same league as many other European allies that buy almost everything from foreign sources.
Now, there is perhaps another way to look at this state of affairs. Look at Australia. Yes, it can produce some specific high-end systems like its new amphibious warfare ships, but it buys almost all its weaponry from abroad, almost all from the US. And it has no problem with this.
The AUKUS deal will theoretically see Australian shipyards learn the trade of building nuclear submarines, but not before the preceding stage in which Australia purchases or leases nuclear subs from the US or UK.
Granted, Australia never had the outsized DIB the UK had and still retains much of. For Britain to adopt an Australian-style procurement strategy would involve some humbling, if not humiliation.