There is a link to geographical numbers for centres on the AMF website in the entry for Ashford. However, the website now lists 0870. 

That's only a minor setback as the Internet Archive stores up websites so you can see what they used to be like. This works a treat in this case. See here for geographical numbers from 6 March 2005. 

Bluebottle wrote on Aug 31^st, 2006 at 7:22am:
I'm afraid then the chances of finding the new underlying geographical number is less than finding a needle in a haystack.

The reason is our search efforts rely on the fact that they've kept their existing geographical number and some other methods.

When a company has gone through all the efforts and expense of getting new geographical numbers and then new 084x/087x numbers that point to these new new geographical numbers then it is nearly impossible to find.  The chances are only a handful of people would know their new underlying geographical number.

Now if only some of the centres have got rid of their old geographical then you could ring one of the other centres and act dumb and ask them have they got the number to the centre you are after.  Sometimes you may get their geographical but it depends on what number the other centres ring when they have a need to ring other centres.  Some company telephony managers don't actually realise that by their own centres ringing each other on their fancy new 0870 is actually costing them more money.  This is all down to 0845/0870 being missold as being local/national rate respectively.