Does anyone remember that BBC programme from 2003 The Day Britain Stopped? Which featured gridlock on the country's roads and chaos at Heathrow after an aircraft going around collides with another aircraft on climb-out.
It was prompted (among other things) by a report which:
"calculated there would be one collision following a missed approach at Heathrow, on average, every 20 years"
NATS' response (quite rightly I think) was that it could not endorse the findings of the report (conducted in 1993) considering that "Heathrow has been operating for more than fifty years without a single collision."
My understanding of is that Heathrow runs very safely, but occasionally, like when a plane shuts a runway by strewing burst tyre all over it safety can be compromised.