Many have taken issue with Metal Gear Solid 5: Ground Zeroes's steep price of Ł19.99 - Ł29.99, but Sony is sweetening the pot by allowing PSN pre-orders of the game to come with Metal Gear Solid: Peace Walker HD.
Unfortunately, the PS4's EU PlayStation Store doesn't even have Ground Zeroes available to pre-order, so it looks like this offer is PS3-only - though we're checking with Sony to get confirmation that this isn't also coming to PS4.
All things considered, this is still a pretty sweet deal. Since Ground Zeroes is a direct sequel to Peace Walker, it's the game most vital to playing before this impending release. I found Peace Walker a noble experiment for the series and noted in my Metal Gear Solid HD Collection review that Peace Walker HD was "not quite as memorable or surprising as its console counterparts," but was "nevertheless a welcome change of pace that complements its console brethren well."
This promotion is only valid until MGS5: Ground Zeroes launches on 20th March.