"David W.E. Roberts" wrote Update - it seems to be perking up a little -
sign of some growth and the
roots have generally turned a healthy(?) green colour.
I understand the roots have to be exposed to sunlight to allow a
beneficial
fungus to grow, which is why the orchids come in clear pots.
However the growing medium includes a lot of sponge rubber(!) which will
presumably hold moisture well, but is the very devil to wet once it is
dry.
Trying the 'plunge then drain' method to see if this works O.K.
Is sponge rubber a normal addition to the growing medium, or is this a
mass
market 'budget' idea.

I'm no expert, David but I have got half a dozen or so orchids on various
windowsills around the house and, like you, I got them from Homebase and
B&Q over the past 5 years or so. According to the labels, they are all
"Cambria" Orchids and these might have different requirements to yours.
[For the more technically minded, it goes on to say that Cambrias are
"intergenic crosses between Odontoglossum, Cochiloda, Mitonia, and
Oncidium." (!)]

I've found them to be surprisingly robust and I water them about once a
fortnight during the autumn and winter and every 2-4 days in the spring &
summer, depending on how warm and sunny it has been. In spring, I give
them a feed of well-diluted "Baby Bio" (usually when I remember, but
probably equating to once every 2-3 weeks).

The main thing it seems is not to let them get waterlogged at the root.
Mine came potted in coarse bark and I've always done as instructed - i.e.
to water by running water through the pot from the top (I do it by placing
them under a running tap) and making sure that all the excess drains away
before putting the pot back into its holder. I've no experience of the
sponge rubber medium, I'm afraid.

Hope this helps.

- Tom.