In short order Dan introduced the Hawks from Yeovilton (were they the top secrect dual engined Hawks?)

Even if the Harrier/Sea Harrier had been available it was the Harriers poor glide capability at the selected flypast height that precluded it from taking part. The Hawk has a greater glide capability.

http://www.pprune.org/military-aircrew/373031-fly-navy-100-a-3.html

From the MOD. Issued at the time of the 2007 Falklands 25th flypast.

‘Harriers will not take part in the flypast over London because single engine aircraft without the capability to glide in the event of an engine failure are not permitted to fly low over central London. Were they to take part, they would have to fly too high to be part of the display.’