At LHR arriving IFR flights are still separated horizontally by distance and not time (...yet). High winds mean a strong headwind component on approach which means a slower groundspeed therefore it takes longer to fly the separation distance. The result is a reduction in movement rate from around 40 per hour to nearer 30 per hour with consequent delays. Each aircraft would be nearer 2 minutes apart instead of around 1 min 40 secs.
If arriving flights could be separated by time (as departures are) then the flow rate and runway utilisation rate could be maximised to suit runway conditions. It would mean getting a following aircraft to (as an example) "fly 1 minute 40 seconds behind the (type) ahead".
(Edit: Sorry HD, slow keyboard skills....!)