Alan, Sir Christopher Cockerell was used as spare parts by Hoverspeed years ago when the SRN4's were still running.
"Maggie" and Anne are still sitting there (went past today actually) it seems the new owner hasn't actually done anything with them or their engines yet as far I've heard. (Someone please correct me if i'm wrong on that)
Sir Christopher (she wasn't called Christopher Cockerell) was broken up at Ramsgate (I think) in 1991. This was when the Seacat's were introduced and the Hovercraft service reduced to the two Super 4s.
Maggie and Anne are still at Lee-on-Solent awaiting their fate.
All the spare engines were bought by the owner of the blue yacht (I forget the name) that was moored at Gunwharf for ages. The yacht was originally built for Stavros Niarchos and had Gas Turbine main engines. The current owner wants it up and running at 50 knots again!