The price is simply down to ASA (Advertising Srandards Agency) rules; you can't advertise a discount in the UK if the product hasn't be for sale at the higher price for at least 28 consecutive days during the last 6 months.
They will list it as £349 for only 28 days for sure, and then list a huge discount in percentage terms. If they reduce it to £249 then a 28% discount reads better than a 16% discount (from £299).
It's not that simple for online retail, the ASA guidelines mean that you can actually put a price up for any amount of time, and then say it is reduced by X as long as the amount of time it is lower than it was higher, e.g. 7 days at £349, and 6 days at £299 is allowed.