When you fill in your forms for BR - you can list your vehicle as a "tool of your trade" you can then discuss it with the OR. The OR won't put you in a position of being unemployed so they will take into account the importance of keeping this vehicle. It may be worth looking on autotrader and arming yourself with the low end values for this vehicle - it may be lower than the £3k you have posted and nearer the £2500 figure the OR seems to like!
There does seem to be a slight variation accross the country, which is a little bizzarre as the OR's all work to the same guidelines. In my experience, a van worth £3k which is needed for work will (more than likely) be ok.