Regardless of what the regulations force you to do, it it still a good idea to add RCD protection to your installation where it does not currently exist.
@GinGaz you are correct all new work installed into a location containing a bath or a shower and also any addition to a domestic lighting circuits require RCD protection.
It is fine to use SY cable in a fixed installation. It can simply be noted as a departure from BS7671 on the EIC. As securespark has mentioned, it is not suitable for use outside without additional protection.