Thanks for posting more information. I found a website
http://www.hpa.org.uk/chemicals/npis.htm which says there are 6 npis centres in the UK.
Clicking on the CONTACT US option on the left, it then lists all the centres. If you go down to the National Poisons Information Service section it then lists the individual 6 centres. Or alternatively, you can click the links for the centre you want by using the map of the UK which is on that main screen, before you click on CONTACT US. I clicked on the london one and it lists an 020 number.
I don't know which location you are more interested in but hopefully this will help you. I don't know if these individual centre's telephone numbers are available 24 hours a day though, and you may have to use the 0870 number for out of hours?
Please let us know if this is what you were looking for.
Thanks.