snip

| You should consider a 6A lighting circuit for upstairs, a 6A lighting
| circuit for downstairs and a lighting circuit for exterior/security
| lighting. If you are planning mains smoke alarms and burglar alarm,
| don't put these on a lighting circuit, put them on their own 6A circuit.

Often better put on a lighting circuit, where loss of power will be
noticed
more quickly. Battery back up smoke alarms are mandatory on a shared
circuit
though.

Owain

I guess it's a matter of opinion. The On-Site Guide allows either method.
I definitely wouldn't put smoke alarms on a security lighting circuit
though.

The problem as I see it is that often, when a light bulb pops, it takes the
breaker out with it.

So, if you are away from home and have left some lights on (or something
triggers the outdoor security light) and a bulb blows and takes out the MCB,
then your smoke alarms will be off as well.

Of course, if there's no one in to hear the alarms go off, then your house
will burn down anyway ;-)

FWIW, battery backup is mandatory, whatever.

Smudger