Hi Julia
My 10 pence worth....
Had a car dumped between me and my neighbours house...the DVLA moved it after three weeks. It was UN taxed/mot'd/insured, not sure if your said vehicle is so, you mentioned a SORN! police not interested, very polite and helpful but not their problem, speak to your city council or the DVLA, which I did every other day for the three weeks!
Most helpful guy was the chappie from the council in charge of "dept' of dumped vehicles! as previous guy said if it's unlocked (which it was) and not able to lock it from inside it's classed as a fire risk and the council send a guy out to check it and report back...also if the tax is over a month out of date it's a DVLA issue!
I went on the DVLA site and reported it and spoke to them just to make sure! alas though their reply was a bit vague, just quoted me how many cars they had to deal with and couldn't say when it might be moved!
I guess as we all know, it's speaking to the right person!....council fellow said he'd try and speak to the DVLA and assume he did, it was moved.