This can be applied to a few Xbox One/360 games but if you change your region the price also changes.
So for the xbox one the easiest way to take advantage of this is to change your region to US. Sniper Elite 3 in this instance is 49.99USD roughly 29.95GBP - a lot cheaper than the UK store price.
To pay for the item you will need to add a US address, just find any old one and then purchase 50USD worth of Xbox live points from one of the many sites available.
You can also do this to purchase items that aren't available in Europe on the store. Switching back afterwards restores your payment details to your UK ones and you can continue to play the games from the US store.
May be helpful to some.