I was pretty sure this was illegal, and I'm sure there's a Highway Code ruling about how far from a junction you should park, but this 'catch-all' should be enough from the Highway Code website.
You MUST NOT leave your vehicle or trailer in a dangerous position or where it causes any unnecessary obstruction of the road.
[Laws RTA 1988, sect 22 & CUR reg 103]
I'm assuming that having your view blocked is an 'obstruction'. Trouble is, people tend to see the lack of any yellow lines as a go-ahead to park where they like these days. I'm guessing he's also blocking pedestrian access to crossing the road too.
I think it'll depend on your local conditions as to who you report them to. We've got local parking enforcement wardens - I'm sure they'd love to photograph him and have him 'done'.
Post script - just found what I was looking for!
"DO NOT stop or park
* opposite or within 10 metres (32 feet) of a junction, except in an authorised parking space"
That last bit is really annoying - it's OK for councils to mark out parking spaces within 32 feet of a junction when it suits them and they can charge residents for a Controlled Parking Zone permit (no I don't live in one). Richmond bring theirs to about 10 feet from the corner when they feel like it.
Of course, if they just painted double yellows around every corner for the first 32 feet, then it would all be so much simpler.