TT system

Sparkingchip:

? No, they are not double insulated, they are insulated and sheathed 

But ... they are considered to be ... in this particular case. The OP's question is clearly covered by Regulation 531.3.5.2.201

531.3.5.3.2.201 For Class I enclosures in TT systems where RCD protection is used on outgoing circuits, double or reinforced insulation of all live conductors (incoming cables, extension terminals, etc.) on the supply side of the incoming device, e.g. main switch, shall be used. Insulated and non-metallic sheathed cables are deemed to meet the requirements of double or reinforced insulation.

And, as others have already pointed out, this means that no other protection against contact with exposed-conductive-parts is necessary [to comply with BS 7671] because of this.

Sparkingchip:

? No, they are not double insulated, they are insulated and sheathed 

But ... they are considered to be ... in this particular case. The OP's question is clearly covered by Regulation 531.3.5.2.201

531.3.5.3.2.201 For Class I enclosures in TT systems where RCD protection is used on outgoing circuits, double or reinforced insulation of all live conductors (incoming cables, extension terminals, etc.) on the supply side of the incoming device, e.g. main switch, shall be used. Insulated and non-metallic sheathed cables are deemed to meet the requirements of double or reinforced insulation.

And, as others have already pointed out, this means that no other protection against contact with exposed-conductive-parts is necessary [to comply with BS 7671] because of this.