From the sounds of it what you call two loops..
was in reality two protective devices supplying power the the same section(s) of cable..
So if one protective device was turned off, some part(s) of that circuit, (typically neutral conductor), could still become live via the other protective device..
This is a serious safety defect and does not comply with wiring regulation 314.4.
These types of problem are made safer by either...
(a) additional wiring installed to correct the wiring error..
Or
(b) combining both of the live feeds that supply the shared section of cable onto the same protective device..
Sounds like the electrician has opted for option (b)..
If you are still using incandescent lamps the chances are they are cheaply produced and imported back to UK,
and lack the internal lamp fusing that historic UK manufactured better quality lamps used to have..
Which are almost certain to cause tripping problems for modern MCB's / RCBO's when the surges during lamp failure can get quite large.
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