Amazon UK offers Back to the Future: 30th Anniversary Trilogy on Blu-ray Disc for $12.41 (£8.49). Add it to your cart and proceed to checkout to drop it to $10.34 (£7.08). With $4.50 (£3.08) for shipping, that's tied with our March mention and the lowest total price we could find today by $8. It includes all three of the Back to the Future movies and includes deleted scenes and interviews with director Robert Zemeckis.
Of note, this item is eligible for the $1.46 (£1) movie credit promotion, listed here.
This Blu-ray set is region-free; the movies themselves will play on US Blu-ray players, but the extras and special features may not.