Thanks - I should perhaps note that I have had the phone for nearly 4 years.
Bought new on contract, then upgraded 2 years later, and the newer phone (S4) is coming to the end of the contract.
Sadly, I may plump for an S5 as the replacement because it still has the exchangeable battery and the external storage which both seem to have gone out of fashion these days.
I forgo the latest Android, but that happens quite soon anyway.
Cheers
Dave R