Light switch for garage loft

[OXFORDMG]

I have a detached double garage fed with underground armoured cable and fuse box by the builders when the house was new.
In the garage, there are 4 flourescent tube units (linked in series with 1.00 T&E) switched from two switches, one between the garage doors and one at the doorway into the garden.
One of the flourescents is in the floored roof space and comes on with the other 3 units when either of the switches is activated.
That's a bit of a waste of energy and I would like to be able to put in a seperate switch to handle this flourescent.
Can I just add a switch in this supply cable to the unit in the roofspace or do I have to disconnect the current feed and run a new switch to the fuse box along with a new supply cable?
Any comment would be appreciated.
John in Oxfordshire

 

[EFLImpudence]

(linked in series

Parallel

Can I just add a switch in this supply cable to the unit in the roofspace

Yes, but it will only come on when the other lights are on - but then, you won't have to go back up when you forget to switch it off.

 

[OXFORDMG]

Thanks for that. I was hoping that would be the case.
And, yes, I should have said parallel.

Thanks again for the quick response.
John in Oxfordshire