electric towel rail - part P legality?

Probably...

but not by refitting the towel rail! ;-)

Like for like replacement, even in a "special location" is fine.

(BTW Zone 3 ceased to exist in the 17th edition).

"Replacement, repair and maintenance jobs are generally not notifiable, even if carried out in a kitchen or special location or associated with a special installation.

Basically you can DIY everything - however some things are notifiable.

i) Replacing a CU is notifiable - but not a damaged enclosure. ii) Adding a new final circuit in a kitchen or across garden is notifiable - but not replacing a rotted SWA which crosses a garden. iii) Adding a new socket in a kitchen is notifiable - but not replacing a socket and crimping on new cable which has been damaged by overheating (loose connection, water penetration causing high resistance terminals). iv) Adding a new cooker or shower is notifiable - but not replacement if it is of the same rating as the original. v) Extending any circuit in a kitchen is notifiable - but not if not in a special location eg, in a porch, garage, shed, living room etc. vi) Adding an outside light on a garden wall is notifiable - but not if it is attached to the outside wall of a house. vii) Adding a prefabricated "modular" systems (for example armoured garden cabling) linked by plug and socket are not notifiable providing the products CE-marked and that any final connections in kitchens and special locations are made to existing connection units or points (possibly a 13A socket outlet). That is a very amusing one.

You can download SI2006 on the ODPM website, hopefully someone shuts that department next.

Thank John,js.b1 - looks like I can do most of the replacement things I have planned. Ta for this feedback.