I said I knew the reasons for the segregated mode which doesn't imply I thought it was a safety issue. The point I made about other airports was to pre-empt replies about the safety issue. Perhaps I should have put that point in a different sentence.
Staggered parallel arrivals are used from time to time. The distance between the runways is just 50 metres short of the international standard mentioned by LookingForAJob.
At SFO the distance between runway centre lines is less than 250 metres with the added complication of parallel take off on two runways cutting across the two landing runways at ninety degrees. Taking off at night towards Oakland Bay, sitting on the right hand side of an aircraft is always an interesting experience looking at two sets of lights heading towards your aircraft and being conscious of another aircraft also taking off next to you.
It would be interesting to know just how much more difficult that sort of operation is compared to slotting in take offs at LHR between parallel landings.
If and when a third runway is built at LHR it will be interesting to see just how the government of the day handles the flack that will be heading its way when parallel operations become a norm.
In the meantime, given climate changes and the increasing frequency of stronger cross winds, delays will continue and there is absolutely no prospect of a runway angled to deal with the problem.