So as with all such jobs, it would be a lot easier the second time around based upon experience.
Thanks to
@mjheathcote and
@Zep for the advice.
Replacement part:
Herth & Buss 75605151 Flasher Unit from Autodoc (
https://m.autodoc.co.uk/herthbuss-elparts/7560531). Price varies but ca. £35-40 incl postage
Tools I needed (because the relay fit was extremely tight):
8mm deep socket (although not absolutely necessary this was a nice to have)
Extension bar
Ratchet
Screwdriver (to lever the relay out of the connector block)
6" quick grip mini bar clamp (to 'encourage' the new relay into the connector block)
Various sockets to remove the carpeted cover from under the steering cowl
In my case there was no way the relay could have been removed from the grey connector block without dropping the loom it is attached to.
In order to do this, I had to both remove the nut that holds the relay (and one end of the blue 'ecu' in the photo below) onto the bolt and also loosen the nut holding the other end of the 'ecu' in order to give sufficient movement to drop the 'ecu' first off the bolt so that the relay could be lifted out too. I found an 8mm deep socket made the re-attachment of the nut afterwards a lot easier than using a regular socket.
I can see from
@mjheathcote 's photo that the metal 'prong' on which the relay connector is attached is sat on top of the 'ecu' rather than underneath it as in my case. Maybe someone has fiddled about with this in the past or Luigi did it in a different order one late Friday afternoon at the factory.
Once the loom was dropped, I had to gradually lever the relay off the connector using a screwdriver going round each corner in turn.
Fitting the relay was fine, except the tightness of the fit meant I got to about 5mm to go and could not get further. Using a mini bar clamp and gently easing a bit at a time going round each side in turn got there in the end.
A 'simple' enough job, that was extremely uncomfortable to do as you lay on your back in the footwell looking up.
Judging by the state of the cover, I am not the first to have removed it but those who have done so previously have been less sympathetic and tried to pull out without removing the retaining nuts first. So I will take the opportunity to patch it up a bit first before I put that back in.