This is a pretty good deal considering Leyland paint is one of the best trade paints you can get - forget the own brand basic stuff that is like water, this is proper good thick emulsion.
B&Q are currently doing a 3 for £40 deal - usually £20 a tub, and these are the 12L tubs, not the 10L tubs.
This might be nationwide, I don't know, but in Sutton in Ashfield yesterday if you join the B&Q club you get £5 off a purchase of £40 or over, AND you get a £5 voucher emailed to you (£30 spend applies).
So, all in all, I have 36L of Leyland Trade White Emulsion for £35.
They also have the standard Leyland "domestic" 10L tubs of emulsion for £10 in Magnolia or White (but no white available at Sutton in Ashfield - your mileage may vary)