Thanks for your replies, it is really good to be able to get other perspectives.
I have made some progress and have got my 100m pace down from above 3.0 down to 2.5.
Went through 'Shinji's Open Water Speed Up' and am not spearing so deeply and have used the catch set up that he recommends.
This works well and has allowed me to get a higher stroke rate going.
Yes, FP of course, I usually rotate through these as I am swimming and after maybe get a CT (choc top)
@Salvo. Lake Albano looks like a place I should swim next time I am close to Roma.
Have swum in lakes Bracciano, Transimeno and very briefly in Como (cold, polluted and speed boat dangerous)