It's certainly an interesting scenario. One thing that caught my eye was the dialling code for London as 020 7xxxxxx doesn't come into use until the big number change of 2000; at the time of the scenario it should be 071 .
If you want a detailed look at the UK dialling codes then you might find this useful:
https://en.wikipedia.org/wiki/List_of_dialling_codes_in_the_United_Kingdom
I'm honoured that you want me to have a look at your next project.