The back yard isn't big enough for a 40m dipole so I measured out some speaker wire for 20m and have strung it between the window on the first floor at the back of the house, to a painter's pole on the fence (which holds the balun), and the corner of the garage.
Quickly I had received stations in New Zealand and Perth. My first transmission, with 10W is shown here on the right and I'm clearly getting out well. I've reduced power to 5W now.
This is great news and I think the dipole can be improved by suspending one leg from the tripod on the garage roof that holds the 2m/70cm vertical. You can see the dipole here, not great, but working.
If the interference comes back I will go for a walk again and try to find it. Even if it's back it will have less effect at 14Mhz than it did at 7Mhz so the move to a higher band will help there. Amazing that a small wire antenna in a tiny back yard get connect me with the world.
It's now Monday night and the terrible interference hasn't returned so far. I'm happy with 20m WSPR results except that I can't get to Sydney so far. Lots of contacts to North America.
3pm local time is best for 20m DX by the looks of it.