A search of the internet reveals an old address with old geographical numbers that no longer work.

However, a search of the unverified list reveals
Out of hours this rings with no answer.

The two 0870s ring for about 20 seconds and go to an answerphone message, the same answerphone message.

I've tried 020 8544 7200 to 75. Many ring unanswered, some have answerphone messages saying press 0 for sales. This may be the operator (switchboard), who is presumably on the above number.

Of the 75 I tried, two have the same message as the 0870s, they be 08 and 10. It's a case of ringing them and asking which they are.

I found 3 fax machines on 25, 26 and 29. When I rang the 0870 fax number after ringing the geo fax, it rang. I then rang the geo fax back and it said it was still engaged. Presumably the fax machine was still on the line, which suggests that none of these 3 are the one the 0870 connects to.

Feel free to carry on after 75. However, I found that 41 onwards rang with no answer.