The Worthing CTA (I'm assuming you are talking about Dover - Cap Gris Nez, New Bloke) starts at FL65, so FL55 would be the preferred level for me, conveniently this works both with our quadrantal rule and the French semi-circular rule as well as transition levels in both FIRs. That (FL55)should give you about 8.5nm glide if the donkey stopped. If you coast out over Dover Harbour, Cap Gris Nez is 17.6nm (9 mins at 120kts in still air). Each of us assesses risk in their own way but I personally do not see that crossing as a *huge* risk...
Cheers
Cahlibahn