Personally I think the response was totally reasonable. Do you really expect the police on duty to go find the file with the listing of all dangerous animals kept in the area (if they have such a file?) and check it? Meanwhile leaving the cat to disapear and possibly kill someone. You certainly can't expect police to personally know what tigers are kept locally, unless they have a personal interest in tigers. Even if they know there's no tigers of that description kept legally nearby they have to assume it could have come from an ilegal keeper. It could have got loose from such a person, or even been released, possibly by someone out of the area. Also again, this is policemen, not experts. They probably know there's rumours of big cats living wild in the UK. They probably don't know the areas or species. Many police probably couldn't identify the species.
Hearing a report of a possible big cat any zoo team is going to be going out and not wait for confirmation: they know what delay could mean, and they know the police can't be relied on to know what they are doing in this specialist situation.
And the general feeling would no doubt be that this is not a wasted trip: everyone involved just got a training exercise for the real thing (not that that would justify this if it was a deliberate prank).