Number on 1980s adverts

[GMH]

Looking at some clips of old adverts over on You Tube, many companies from the 1980s, always seemed to use the same telephone number in their adverts, which was 01 200 0200. Could anyone please tell me what kind of number it was if you dialed it? Was it similar to the 100 Operator service where you ask to be put through to the right company, and is an equivilent of that number still goimng today? It seems bizarre that so many companies shared that same number.