I used to have TT overhead cables from poles to my house and a earth rod under my paving slab, 10mm to earth block next to fuseboard ( as part of upgrade for electric shower in 1995 ) a few years before the electricity Board remove all poles and rerun new cables under ground in my street. I had a pole in my back garden and they used to pay a small fee for siting their pole in my garden, now stopped.
They ran it from road to my house wall and up to connect to existing cables.
I still have a old rewireable board as earlier post. ( I still haven't start yet as I have been advised to call Building Control first )
Do this count as a TT system?
Possibly, where do you get your earth from now? Is it still from the earth electrode or is it from the suppliers cable?