As per instructions I tried to update my profile on my home page, to get personal replies. It kept coming up that they already had someone with those details. It was me !
I will never understand IT if I live to be 100.

Without knowing the variety, it's very hard to give general advice on Orchids as they originate from all over the world and therefore require different conditions to live.

If i was to give some general advice, i would say that the plants should be kept slightly on the dry side during winter and out of centrally heated rooms. Aim for 10-15 deg C at night and try to keep the humidity up a bit. They'll enjoy bright conditions out of direct sunlight.

Any chance of a photo ?

Majority of GC orchids are phalaenopsis.
The 'official' aftercare will go something along the lines of plenty of light but not direct sunlight, keep moderately moist, feed once a month.
Temperature shouldn't be too much of a problem but avoid keeping them in a room where the temperature moves about a lot (ie hot in day, cold at night) try keeping temp as even as possible.

Keep it in the (clear) plastic pot but stand it inside a ceramic orchid pot - these have a ridge about an inch from the bottom to the pot narrows, to allow water to drain down and provide the orchid with a bit of humidity. Best way to water them is to dunk them in a bucket full of warm (room temp) water for about 10 minutes once a week in the growing season, once a month through winter.

If it lasts through the summer, it will want to go somewhere cooler over the winter.

Thank you Urbanite - its almost dead now.
I did keep it in semi shade, and put rainwater in the
saucer. Wondered if it had been kept too dry by
the supplier.
Flowers and leaves have fallen off. Waste of £8.
Its been in a warm room for a week. Maybe the
dunking will induce it to make some growing shoots.

I have put it back into the polythene cover - hospital
job.

Spritzhenry did a blog on orchid care a while ago, you may be able to find it still.

Orchids don't want to stand in water,Diane..they need a good watering,then allowed to drain fully,and then ideally stood on a base of gravel, to help to create some humidity around the plant..the buds and flowers could possibly have dropped off,with the change of temperature,transporting it from the GC to your home..and the warm conditions for a week in a warm room..I think you have given it far too much water..and when you say you have put it back in it's polythene cover..do you mean the one they are wrapped in,when you buy them,or the plastic see through plant pot? If it's the first one,please take it off...it's only to protect it,till you get home..
Don't despair,let it dry out,and only water when the roots are a very pale green..this is your guide to watering as suggested above..if they are a mid/bright green,leave well alone..

A cooler window with good light,is preferable...
You may think it is dead,but be patient,as it should throw at least one new stem out ,sometime in the coming year.As long as the leaves look green and healthy,which benefit from a misting now and then,to create the humidity they get in the wild,it may be ok..and an occasional liquid feed ,will help..
Mine only throws new stems out around June every year.,but lasts till Christmas.,and it's coming up to it's 10 year....good luck..

I have just seen Sbg's comment about a blog Spritzhenry posted,and found it for you..
titled.Awkward Orchids' dated 25/10/2009...It is invaluable advice,and I used it myself...thanks Sbg for the reminder :o)