Evening: back with update on the creaks!
Happy to report that the creaking has stopped. I feel I should be paying somebody for the good advice
I have greased the handlebar screws, the stem, also tighten a bit the nut that holds stem and allows to raise handlebars. It turned out this was a bit loose.
Ride to and from work were creak free all the way.
I had a look in my collection of tools, some of them inherited from my late partner: a torque wrench is amongst them. Haven't got a scooby how to use it, but I will learn, same way I learned to change a tap on a sink, a tyre on a bike
Thanks again all for your help