How should my light be connected to this old wiring layout?
In the UK colours are as follows

           old UK colours   newer EU colours
live       red              brown
neutral    black            blue
earth      green            green/yellow


The switched-live from switches is often insulated with the neutral colour (e.g. black) and should have red tape over it to indicate it is switched-live not neutral.

Your problem is that, to make sense of wiring, you need to carefully study the wiring before you remove a fitting and make sure you understand how it works. It can be difficult to do this after the wires have been removed from the fitting.

In some cases, a lot of the electrical wiring is done inside the casing for long fluorescent light tubes. This can include wiring for other light fittings in other parts of the room or in other rooms.


  The problem is at some stage there were two switches for the light


Typical UK 2-way switch wiring is as follows



The image shows a pendant light, but the same principle applies for a fluorescent light. In your case you have the old-colour wiring for the fixed wiring in the walls, nopt the new colours shown here.

The earth wires here are shown green but they are often bare copper - the installer should have added a green/yellow sleeve to them.

Note that you do not connect all the neutral wires together and you do not connect all the live wires together.



If you need more detailed help, take a clear well-lit well-focussed photo of the wiring at the ceiling - and of the wiring behind the associated switches. Edit the question to insert the photos (or insert URLs to public websites where you uploaded the photos)