No. If the fuel costs were exorbitant the channel ferries would have eaten them alive. What actually happened is that the Chunnel, which is rail and cheap, knocked hell out of both conventional ferries and hovercraft which cost more to operate. If I remember the old reports correctly it was the maintainance costs that were the sticking point: ship hulls are more of a sunk cost than regular skirt maintainance and gearbox repair.