Hi Gonzo,
Background to my remarks, and with the caveat that I retired in '99 and am an old fart so things may have changed.
ADGE radars
In the days of the T80/84/85 static radars these could be used by MATO/NATS, because they were static and had had extensive polar diagram/trials coverage.
When we introduced the mobile T91/92/93/102 series, with multiple mobile sites, these were not considered usable Which is what lead to the death of Highland and Border radars and the the co-ordination suite at Neatishead as a consequences.
NATS radars
When they started to feed in the NATS radars to UKADGE the MoD shut down Portreath, Ty Croes, Bishops Court etc. About 4 years later NATO found out the replacement sensors were SSR only and went ballistic. They didn't give a damn about the UK east coast, but the periphery had to be covered, so we had to move radars back again (which meant robbing the east coast sites so they were left with the T93s (crap and not fit for purpose) and the NATS feed.
The problem with the NATS feed being they were mainly SSR (at long range, the short range primary for airfield control not be fed, only the SSR), and even when the primary failed there was no indication.I had many occasions when I suddenly realised I was controlling above 245 in the MRSA using SSR only.
ORAC: IC, FA, MC, IDRO. TPO, RO 1975-1999.
NATS area survillance radars do both primary and secondary.
Bishops Court was closed in July 1990 because of the cost of force protection after the place was mortered by the PIRA in Sept 1989 and the gap in coverage was covered when the Wattisham T94 was installed at Ty-Croes in July 1991 (though not operational until late 91).
Type 91 radars were sold aboard I do seem to recall and the Type 93's were kept because they were suppose to be better against ECM. After they dealt with the spares shortage on the kit and fixed sited the kits (Antenna in radomes on towers and cabins in shelters), it did tend to be reliable.
When NATS feeds came in during the mid 1990's Portreath lost it's radar and Ty-Croes was closed. Portreath did get a radar back, but that was after the events of 11-09-2001.