Pale Blue Retractable Clothes Line in the "Sainsbury for home" range.
I think they were initially sold at £7.99 and have been successively reduced to £2.49.
I've linked to a picture that matches the shape of this item(but note this one is pale blue!) as I don't think it's available on Sainsbury's online site.
Lowest price I've seen for a reasonable quality alternative is £3.99 at Argos, although Wilkinson's had one at £2.99 that looked very poorly made from thin plastic
I found this displayed on an end unit with other clearance stock (including bathroom scales) in my local superstore but they were originally displayed with household items like dustpans and pegs, so may be in either location if your store has them.