Quote:which numbers?
02072418600, 02072418601, 02072418602, 02072418603.... etc etc
I suggest you make a note of what you get on each number, eg fax, no answer, out of service, busy etc. Also, make a note of which answer as someone's personal extension number, ie where you get an answerphone saying something like "This is John Smith, please leave a message..." Those numbers are presumably not the ones you're after.
*Hopefully* (although not always) some will answer with the same messages as the NGNs, that way you know (or can be quite certain) that these are the geographical number(s) that the NGNs go to.
This is how we've found some of the numbers on this site. Often, switchboard/reception numbers start 00 and other direct dial numbers follow on. OK, so it doesn't always work, and you may get another company/residential, but it's worth a try. You may also have to ring through several hundred (or more) numbers, depending on the size of the company.