For something supposedly "Moved to Electrics UK" it still seems to be in the "outside" forum.
very old wiring
In which case maybe the first priority would be to replace the house wiring for safety's sake ?
The wire colours you mention for the light fitting are not one's I usually see. I'm wondering it if is a foreign fitting, in which case you need to be sure it is suitable for connecting to the UK supply before you start. * If it is designed for 110v or something it may be dangerous to install here. *
I'll make a stab at what the present wiring is, anyway, but if you don't know how to check you are probably better of calling in someone who knows to do it for you.
I'm unsure about the description. Through one port ? Do you mean connected to a single point ?
You should (probably) have 3 cables, each with one red wire, one black wire, and an earth which is un-insulated until someone adds the green/yellow insulation themselves. You may also be able to see a flex which used to connect to the lamp fitting. Making 4 in all.
One cable will be the mains supply to the light fitting. Another will be taking the mains supply from this light fitting to the next (may not exist if this is the last light fitting in the "chain"). And the last cable goes to the light switch.
and 3 green earths crimped together and tucked back
Dealing with the earths first, they have to be connected together to ensure the earthing system goes all around the house. If your light fitting has an earth terminal the they should be connected there. If it is a metal fitting it should definitely have one and you do say that the fitting says it must be earthed. So it looks as if you need to connect it to the earth wires.
3 red wires all fed thro' one port (?)
The 3 live red wires will need to be connected together. Mains in has to go to mains out (if it exists), and to the light switch. Live does not go to the light fitting (unless a special terminal(s) has been provided for them). You don't want the light to be on all the time, so live goes to the switch first.
2 black wires - 1 of which has a narrow piece of red tape around it - fed thro' another port,
1 single black wire fed thro' the last port
The description of the 4 neutral black wires throws me a little. This is because you seem to suggest that the black wire with red tape is connected to the black from another cable, whereas I'd have expected it to be connected to the live red wire in the flex, to the lamp. This is because I'd have thought that the black with red tape was from the switch, in which case it is not being used as a neutral, but a switched live (i.e. is disconnected when the switch is off, but goes live when the switch is on). It normally goes to the red live wire in the flex to the lamp. Since this confusion is about whether something is live of neutral, you would need to check all that to be sure. Connecting live directly to neutral tends not to be a good idea, even on Nov. 5th.
The other 2 black neutrals are possibly from the mains in and mains out cable (if it exists). They would connect together, and to the neutral in the flex to the lamp. (Maybe it is the flex black wire that you are referring to ?)
As for the unit, I stress again check it is compatible with the UK system. I'm just an enthusiastic DIYer but I'm nervous about guessing too much about wire colour codes I'm not familiar with. Of course it may just be that the manufacturer chose their own internal colours, but ... Maybe you'd be well served by searching for the unit of the Net to see if you can find instructions ?
Just taking what you told us as accurate it seems ...
blue/white wire is fed into Mains By mains you mean live ?
red/white wire fed thro' same as well as Live port, A second live ?
black/white wire is fed thro' Neutral Neutral ?
its Earth port states that it must be earthed. Earth ?
But to be honest, without the ability to check that out I'd be loath to connect and hope. Might be cheaper and safer to sling it and buy one with instructions ?
