P7 that never was
Y-G
In fact the MOD did in fact go for the P7 in the mid 80's. At that point the Nimrod MR2 mid-life update was considered too expensive so the P7 all in one package, so beloved of MOD PE, was chosen. MOD said no more would be spent on the Nimrod, which is why it was always struggling for funds.
Then the US Navy did the dirty and cancelled the P7 as it did not meet the promised performance spec. The update 4 electronic suit was continued to be added to P3's, but that was also cancelled when it failed to meet its spec.
Having to go back to the drawing board, MOD PE resurrected the same ASR for what became Nimrod 2000 with a few tweaks, which is why to some it was appeared out of date.
Interestingly, I believe the MRA4 tactical suite was not a million miles away from update 4, (Both built by Boeing), however, now it had a processor up to the task.