While a radial socket or shower circuit may be called upon to deliver the full 32 A , there will be almost no lighting circuits on a 6A MCB that take anything like the full 6A, and probably in many cases not even an amp. 

Arguably a 20A JB should be fine on a ring of sockets, as 20A cable would be accepted though I prefer to see 32A.

Given the true load is fixed, and low, the rating of a lighting box is a bit of an irrelevance, as the real question relates to how many wires can be inserted without it failing to do up properly and is it in a sensible place to inspect. 

In recent years I have been moving towards screwless fittings as vastly more reliable than things with little grub screws that someone either fails to tighten or cross threads so they feel tight but are not gripping.

Mike.

While a radial socket or shower circuit may be called upon to deliver the full 32 A , there will be almost no lighting circuits on a 6A MCB that take anything like the full 6A, and probably in many cases not even an amp. 

Arguably a 20A JB should be fine on a ring of sockets, as 20A cable would be accepted though I prefer to see 32A.

Given the true load is fixed, and low, the rating of a lighting box is a bit of an irrelevance, as the real question relates to how many wires can be inserted without it failing to do up properly and is it in a sensible place to inspect. 

In recent years I have been moving towards screwless fittings as vastly more reliable than things with little grub screws that someone either fails to tighten or cross threads so they feel tight but are not gripping.

Mike.