Hello Evan and Mick and first many thanks for your support.
Evan your final comment on wiring made me check it again after checking several times anyway.
I have found and corrected the problem and now all works well.
For the 4 x connections from the Nextion Display to the Nano Board, I was following the pictures in the Barbaros WB2CBA article.
The connections are at 1, 2, 5 and 11 on a 14-pin header strip.
As per Barbaros recommendation, I used a right-angle male-to-male header, broken off a 40-strip to match the header on the Nano board.
Connecting the 4 wires to this right-angled header, for pins 1, 2 and 5 I counted from one end, and for pin 11, I counted back 4 from the other end,
That would have been fine if my angled header strip had 14 pins, but mine has 15 pins.
The header strip on the Nano board, on closer inspection, has nearly 15 female sockets. It has just been badly snapped off.
I had snapped off my angled header to match it at 15 pins, so counting back four, I was connecting the Blue wire to pin 12, not 11.
I put it on Pin 11, switched the radio on it and works fine. Something for others to watch out for also.
Many many thanks for your great support.
By the way Evan the date for returning my Nextion to Amazon UK was yesterday!
All the best from the UK