Get any satellite imagery of the UK, like on Google Earth. Even at a very zoomed out level, with London and Birmingham but an inch apart, you'll instantly spot the bit of HS2 they're building.
To this point; if you look at google maps satellite view and zoom in/out repeatedly over the UK the yellow line 'road' that doesn't disappear and reload is the construction site of HS2.
If you want confirmation, the easiest bits to "check" are Aylesbury and Coventry. London and Birmingham are too big for the features to stand out.
To be clear, it is currently really easy to find because major earthworks are being done, and that requires space to move in the equipment to do it, along with new roads to get to points that were previously inaccessible, being the middle of nowhere.
To see what it will look like afterwards, try to find High Speed 1, aka the Channel Tunnel Rail Link, now that it's had nearly 20 years to be landscaped and vegetation to grow back. If you don't know what you're looking for, you won't see it.
