Thanks for your responses Steve, Graham, Arthur, and Michael
I had chickenpox at 14 years, thinking at first it was a crop of acne ! So far I've opted not to have the shingles vaccine.
Chickenpox vaccine is NOT routinely offered to children in the UK, as the infection is usually mild, and " natural immunity " is preferred. The rationale is that natural infection in childhood is preferable to adulthood - when both chickenpox and shingles are more likely to be severe. " Routine " vaccination might mean those reaching adulthood who had NOT been vaccinated could therefore be more at risk, if they then got infected.
Routine vaccination against chickenpox IS offered in other countries such as Australia and USA. The UK policy will now ( again ) be reviewed following a recent severe case resulting in a 5 day hospital stay for a 2 years old toddler. Thankfully the child has recovered.