Could be construed that way I guess.
Its not an offence (to obstruct) if it means you will have to break the law to move. You should STAY still. They have the legal right to go around (opposite side) of red lights etc,
YOU don't.
However, as said if there was no choice, I'd do it anyway and...
The van driver is a complete muppet, however consider this.
On an AA forum site.
'You must not break the law to move out of the way for an emergency vehicle, and you will be liable for prosecution if you do. A report in the media some months ago described how a woman driver was picked up by a...