A7700
3nm is the nominal standard minimum radar separation, variable under certain conditions. At Heathrow, 2.5 is the absolute minimum.
I am not aware of an ICAO approval to 2nm to the same runway and I'd be grateful for a reference on that.
"for the annualy few days of real strong headwind, just ask the crews to keep higher indicated airspeed than as long as theA/C can do it and the difference is peanuts...The difficulty is more on the radar vectoring side when, with high wind gradients ( in force and direction) the accuracy of the sequencing from downwind to ILS interception is decreased"
That is just the point. The different speed requirements between types does not permit that and there is a big debate going on about this. A BA B757 will not do 170 to 4DME. Mode S indicates they insist on slowing from 160IAS at about 5DME so that they can be stable by 1000' DH. On the other hand, the Airbuses have this Ground speed, wind-shear protection thing that stops them slowing in very strong wind.
Sound technique should overcome sequencing difficulties. E.g.
1. The use of vertical fseparation until established takes care of significant opposing base leg GS differentials; it means you can turn in tight without fear and then let the GS differential open up the gap.
2. Long final length gives up to about 3 minutes (say between 18nm and 8nm) over which 20kts speed differential can be used to tighten spacing. (That is a full mile of catchup - if you've missed by more than a mile then something may be wrong with basic technique.)
NATS' data investigations show that Gatwick is a little more resilient to strong winds than Heathrow because, operating in mixed-mode, it can reduce spacing to preserve a time interval - Heathrow cannot (legally).
Point 4