It normally takes more than one spray to get rid of red spider mites. I found hot really soapy water got rid of of them - but it took weeks and it was not a nice job as they appeared to be eveywhere in large numbers and the cloth I used was covered in hundreds of them!

I never found the plant infested with them - they seemed to be all over the walls and glass in the greenhouse, so make sure you clean those areas as well as pots.

Thanks kildamorie . I will try this but i cant remove my tom. plants so will have to try not to catch them. What i am really worried about is that we go on our hols. in may for 2 weeks and my friend ( lovely as she is) will water them but not take any notice of these pests so i must be rid of them before we go.

Er, are you sure they are Red spider mites. For a start they are not actually red, more a brown colour and basically, if you can see them then they are not spider mites. Normally one only sees the results of their activities, webs and blotches on the leaves. These red things could actually really be red spiders. Use a magnifying glass and count the legs, spiders have 8 and mites have 10.
If they are red spiders then they will eventually disappear of their own accord, off into the wide world where they are gardeners friends, eating aphids etc.
Agree though they are a bit 'itchy' making when there are millions of them

If it is spider mite, then the parasitic mite in the link below may be of interest to you......

http://www.defenders.co.uk/pest-solutions/biological-red-spider-mite-control.html

A bright red, pin-head sized mite stalking over your plants is one of the many species of predatory mites, and is actually busily eating the spider mites. Cleanliness, coolness, and moisture encourage them, so vigorously hosing off your plants on a regular basis and venting the greenhouse on hot days are a good way to encourage them.