I came into Dover Eastern entrance by ferry last light and noticed strobe lights on each side of the entrance. Is this new or was it because of the low (foggy ) visibility?
VicS is absolutely correct - these high intensity strobe lights at either side of the Eastern entrance at Dover are activated during periods of restricted visibility and are worth their weight in gold when bringing in large ships in dense fog.
Also worth noting that the green/white/green and 3-red IPTS Traffic signal lights positioned at both the eastern and western entrances in the port, have now been fitted with brighter LED bulbs, thereby giving a brighter aspect as well as a longer visual range in poor visibility.
VicS is quite correct in saying that the high intensity strobe lights at Dover's Eastern entrance are for use in restricted visibility. As the name implies, they are designed to pierce through the fog and this they do well in practice (speaking as one who regularly pilots large ships in to the port in all weathers.... including fog!).
It is worth noting that a recent upgrade of the IPTS signal lights (G/W/G or 3 Reds) to LED bulbs at both the western and eastern entrances to the harbour, has also resulted in them being picked up that much earlier in poor visibility. Even at the best of times, Dover can seem quite intimidating for yachtsmen due to the volume of heavy ferry traffic coming and going 24 hours a day, but even in restricted visibility, Dover Port Control on VHF Ch74 can give invaluable advice to ensure that you can enter/leave safely.