I think T8 LED replacement tubes will work in a T12 battern fitting.
Not sure if the slimmer tibe will look odd though.

On Thu, 31 Dec 2020 16:21:20 -0000, "Brian Gaff \(Sofa\)"
wrote:

But what if you don't want to remove a fitting and have to repaint and
decorate everything as were it is was never painted. Can one still, for
example get the led conversion kits that one could continue to use the old
Thorn single and double fittings with 40 watt tubes but with LEDs instead of
the now obsolete tubes. (the fat ones) Brian