Items for sale

Hi
I am trying to find somewhere online where there is a price of legislation that exists for items that are “on sale”. I know that a “sale item” has to have been advertised at a higher price for x amount of days but can’t find anywhere my actual question....
My question is
How long are retailers allowed to say an item is on sale? I.e saying that a TV is discounted by £500 and it remains discounted at this price for three months, surly it is no longer a sale item and the price it is reduced to is in fact the new price and therefore it is no longer on sale and shouldn’t be classed as a reduced item.
Hope that make sense
Anyone know?
I am fed up of seeing the tv and coffee machine that I want showing as “on sale” even though it has been “on sale” for three months. It cannot be an on sale item after three months and surly it is now the price that they want and becomes the RRP!!
Thanks in advance