A bit of realism here. Jersey has a population of 100.000 people. In Durrell's time Jersey was a thriving holiday destination for English families, this market has largely disappeared. I don't know what Jersey Zoo's current visitation is, but given those figures, in any other zoo in any other part of the world, they would be lucky to get 40,000 to 50,000 visitors a year.
I'm quite sure if Jersey Zoo were to obtain tigers, they would be housed adequately and safely. However the reality is big cats are expensive to keep. The battle for Jersey Zoo administrators' is to maintain a collection that engages and maximizes visitation and does not exceed what must be a limited budget.