It's a CU swap not a rewire.

Strictly speaking all sockets should now be RCD protected inducing the
ones in the OP's loft.

OK that is one "gotcha", I did not realise all sockets were to be RCD protected I thought it only applied those with wiring less than 50mm deep in the walls.

Just to clarify the alarm situation. When we first moved in the so called professionally installed alarm was useless. As a temporary measure because we knew the kitchen and bathroom were going to be re-done resulting in quite a lot of disruption and rewiring of the kitchen. I was loathe to start any work that involved major disruption until I had to. The system we bought was a wireless DIY system this meant that the control box and bell boxes each had their own wall wart PSUs. As a temporary measure and to keep the PSUs out of sight and out of mind sockets were located in a convenient place in the loft. These sockets were for convenience sake only for the alarm and wired into the light circuit which was not RCD protected a little naughty but the alarm at best draws minimum current about 200mA if I recall. The CU does not have any spare ways so there was not really much else that could be done at the time.

As well as the CU swap I am doing a partial rewire mainly the kitchen and separating the lighting circuit into two as described above and connecting the garage. The kitchen ring main will be completely new as at present all the sockets are in the wrong places with most of the if not replaced would end up above the middle of the hob along with several fixed appliance switches. Other rewiring involves putting the alarm sockets on a separate circuit instead of the lighting circuit and also the boiler which is in the airing cupboard and utilises the old immersion circuit, a fused spur unit in the cupboard with the feed going via a switch in the kitchen situated above the new hob position, the plan with the latter is to eliminate the remote switch and feed directly from the CU. Whilst pulling through the cable for the boiler I can draw two cables through to the airing including the proposed alarm cable which will be surface mounted in the airing cupboard.

So not quite a full rewire but well on the way. As implied before the CU was replaced sometime before we bought the house utilising all the old circuits apart from wiring in the shower. This left a messy arrangement of junction boxes dangling off cables as a result of repositioning the CU higher. The rewire will eliminate the junction boxes as the new CU will be lower now that some of the clutter in the way is being removed.

Richard