OK have identified the problem
I used A0 for all of the tests
When I connected the temp sensor twig into A0 on a Lotus board - all worked perfectly - so thanks for creating the updated formula
When I used a Grove shield & plugged the twig into A0 we’d get the lower temp values.
It then dawned on me to look at the 3.3V-5V switch on the Grove shield & sure enough it had been bumped into the 3.3V position. Flicking it over to the 5V position & all working correctly!
Caught out by a trap for newbies