I came across a reference in a collected article by George Mackay Brown which seemed to imply a postal strike in early 1971, at the same time as the currency was decimalized. While I clearly remember decimalization (I was 12) I did not recall this strike - and found a fascinating reference.
1971: A different world.
A world in which large trades unions wielded immense and arbitrary power, backed up by the frequent use of instant-walk-out strikes - and where union leaders were household names.
Whereas now the union leaders are unknown and national strikes are rare. Indeed, there is so little 'solidarity' in UK society that it is hard to imagine organized communal action.
And in 1971 the postal strike was compensated by a multitude of private and informal postal services which (over the space of a couple of months) was able to rapidly organize and to deliver two thirds the volume of post as the normal official postal service!
Imagine such a high trust society where so many small groups of people were able to say - give us your money and we will deliver your letter - and people did give them money, and they did deliver the letters!
So, on the one hand the UK of 1971 was one in which there was enough cohesion and organization to organize frequent national strikes, and on the other hand with enough cohesion and organization to react to and compensate for disasters such as national strikes.
Now, the government and very large organizations do everything; and what they don't do, doesn't get done - and cannot get done, because people neither know nor trust each other; and all levels of social cohesion between the state and the individual have become exceedingly weak (except in their power to disrupt and destroy).