Neo,
I am a tad confused. You state you whizzed through the Ishihara plates. That infers that you went through them without any problems - if that is the case, get yourself down to Gatwick and have the Ishihara test because if you pass that then you will not be tested on the lanterns.
If I have misunderstood you, I would still go down to Gatwick, have the full test, ask the optometrist to test you on all plates and tell you how many you got wrong. Keep this information to hand - it may come in useful later. These lantern machines are very old, they are seldom maintained properly and some may very well be better than others - you never know, you might just pass the ones at Gatwick.
BTW, don't worry about the anomaloscope. Many people fail to meet the standards set for the aviation world.