@JammyDodger101 - expanding a bit on @Countmeout's post. Yes, two main sales a year - in June and in December (after last Christmas mailing). These last several weeks (feels like several months) as additional stock then returns are added to site. Usually short sales in March ('end of Winter') and September ('end of Summer'). Sales are online only. If you miss something in a sale, then worth checking next time for returns.
There may be a specific promotion (e.g. 20% off Fair Isle jumpers) but this seems to be random and rare. Toast no longer does regular new season discount offers but a few customers (hens' teeth indeed) might get a 20% off offer (never had one myself).
There are occasional sample sales in shops (seems to be limited to Shepton Mallet and the odd London store), sometimes done for charity. No idea if there is a pattern to this but doesn't appear so.
The more 'seasonally themed' an item is, the more likely it is to end up in a sale though most things end up there. If you are a size XXS or XS, you have a better chance of getting what you want in a sale as larger sizes seem to go first.