Your points expire if you make no purchase for 12 months, whichever loyalty tier you are in. Each new purchase starts the 12 months again.
Once you redeem points for a discount voucher, the voucher expires 6 months after redemption if you do not use it.
For example, if your last purchase was on 10 May, your points expire on 10 May the following year unless you shop again before then. A voucher you redeem on 23 July expires on 23 January if it is still unused.