I can't answer reliably the first part of that but on the "applied
retrospectively" I'll offer a firm "yes if it's a safty issue".
IMO it was yet another cock-up by officials and/or gold-plating by the
safety lobbies advising them:
a. the regulations require landlords to "ensure that the electrical
safety standards are met during any period when the residential premises
are occupied under a specified tenancy;" and
b. define "“electrical safety standards” means the standards for
electrical installations in the eighteenth edition of the Wiring
Regulations,"
c. it was pointed out when the draft regs were published that this
seemed to mean properties had to meet the 18th
d. the official response - rather than to amend the draft - was to say
that "Existing installations that have been installed in accordance with
earlier editions of the Wiring Regulations may not comply with the 18th
edition in every respect. This does not necessarily mean that they are
unsafe for continued use or require upgrading."
e. they have a fig leaf in the way the 18th edition has "existing
installations that have been installed in accordance with earlier
editions of the regulations may not comply with this edition in every
respect. This does not necessarily mean that they are unsafe for
continued use or require upgrading”. But I'd still argue it's sloppy
drafting.
Anyhow, in short you are in the hands of the report. If that says
there's a safety issue (code C1 or C2) you need it done - or a different
report. Code C3 is optional.
--
Robin
reply-to address is (intended to be) valid