[jambutty]

Originally Posted by entwisi

Care to find a link that backs this up? The Highway code (whilst not legislation) doesn't seem to back you up

Certainly!

The Highway Code implies that you should not park where it will cause an obstruction to other road users. It mentions specific instances and in particular at:
http://www.direct.gov.uk/en/TravelAndTransport/Highwaycode/DG_069860

[Laws CSDPA sect 21 & RTRA sects 5 & 8]
242
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]
243
DO NOT stop or park anywhere you would prevent access for Emergency Services

Although the Highway Code is not in itself law most of the points covered by it has laws to enforce the various points.