The odds of manchester, in particular, being "chosen" as the target for another Tunguska are really rather slim. Even if a Tunguska-scale event DOES recur this century (and we're not sure yet if they have a 50-year or 500-year recurrence) there is about a 95% chance that it would occur in a remote or relatively low population area.

The Sky is NOT falling.

Sure, there is a RISK, but it is almost negligible at a personal scale.

The chance of a whole city or a whole coastline being wiped out by an impact is MUCH smaller than the risk of a major earthquake - we get those every decade or so, causing major damage to a moderate-sized city with tens or hundreds of thousands of deaths.

Do we, as a human race, set up a huge infrastructure to research Earthquakes? No, we do it piecemeal and in dribs and drabs. Some countries have lightly-funded seismological institutes, but geophysics is just one nerdy profession amongst many.

let's say, that Tunguska is a 1-in 100 year event, and it will hit a major city with a 5% chance, killing approx 1 million people. That's 500 deaths a year. More people are probably killed by lightning, or falls from ladders, worldwide. It's just a risk.

Now, what IS an unusual risk is a "dinosaur killer". That would kill not just the entire human population, but everyone yet to be born in the future. As such, it clearly requires a plan to mitigate the risk, but HOW much effort? That's the $64 billion question...