Can I use 1mm 3 core & earth to connect sockets

Yes, 3 core is required for 2 way lighting circuits. Personally i always use 1.5mm t&e for lighting, but either 1mm or 1.5mm is ok. With the use of LED lighting so much these days, the load on lighting circuits is far less than previously used, However i would always advise you to plan the intended potential load that may be used, and use the correct size based upon this. Hope this helps.

Hi Tim, yes you can use 3 core for the 2 way, infact you need 3 cores or it wont work as a two way, & you can use 1.0mm t&e for the lighting, for up to 1000w or 1 kw (6A,) as your only connecting up 3 lights ( max 150w,) you will be fine, 1.5mm t&e can take more watts/kw, sould you want to run more than 6A/1kw, genrally not needed on domestic installs..............hope this helps.