I don't see that the comparative reliabilities of the engines is really a consideration, it's what you do if the engine packs up that's the important bit! IMHO the only way you'll see a Seajet in central London is a static display! The only flying Harrier I in the UK is the Qinetiq VAAC however, it doesn't look much like an FA2!
Even if you won the single engine, glide like a brick, it'll be alright over London, argument. I don't see how you would find a pilot that could be authorised to fly one. The airframe and engine are now not supported by an engineering authority either. I can't see an answer to this one in the next 2.5 months! Given the exceptional amount of work still left to do on the Vulcan it'll be a miracle if that is ready either, but fingers crossed!