True enough but (as we all know) insurers will use any possible tactic to refuse a claim.
Picture the scene. The OP installs his nice new fused spur correctly (including RCD on the ring if it wasn't already protected). The cooker hood develops a fault and causes a wee conflagration, writing off the house. Fireman Sam pinpoints the hood as being the seat of the fire.
Insurance company than starts looking for documentation. If the place was built before 2005 (and is all wired in red and black) then they may not find any. However, if there exists a test certificate from construction showing that there was no spur in the kitchen and the spur is wired in modern colours (ie post 2005) then they have a cast-iron excuse to either refuse the claim or reduce it substantially, especially if the OP is on record as the only resident or the only resident since 2005.
There would be a defence of 'work was done to the relevant standards' but there would still have been an absolute offence (notifiable works were carried out without notification). Am I paranoid? Maybe.