Ok, this is a bit complicated.
We trade in wife's car, which has a private plate.
Main dealer, big chain, and sales guy wants the sale to go through yesterday, for end of month, which is only 3 days after we do the deal - fair enough, and we get a cracking deal too
so the normal and easy process of getting the number transferred from one vehicle to the other by the dealer pre purchase and us then simply swopping cars over and paying the money can't happen, therefore the plate needs put onto a retention certificate - still ok
then it goes wrong. Being no expert, and knowing it is a big chain reputable place I ask the sales guy what happens to the tax disc on the car we are trading, as it has 7 months left on it. He says 'you take that and send it back to DVLA, with your V5 slip, for a refund' - so that's what I did, and posted it last night.
Sales guy phones today 'err, we need your tax disc to send with the form to put the plate onto retention, can you phone DVLA and get it back, they can't speak to us as you are still the registered keeper'
So I phone DVLA and they say :
'we can't send that tax disc back, as it is automatically destroyed on receipt'
'you could get the rest of the V5 back from the dealer and go to local DVLA office, explain situation and they 'may' give you a replacement tax disc for £7.....however when they see that you have 'sold' the car they might not' (they will know I have sold it as the yellow slip on the base of the V5 is missing as I have sent it back with the tax disc!
'if you can't get this replacement disc you will need to repossess the car, reregister it in your name, and restart the process of plate transfer' WTF 
I am waiting for a call in the morning from the Sales Manager...
Only things I can think of are going to the local DVLA, with the dealer, who they will know, with as much info on both the cars to evidence what is and was mine, what has been bought and sold and hope they do issue a replacement disc, or, the old car has to actually become registered to the dealer as keeper, rather than going off to an auction with the wife's plate as part of the sale, and then it gets transferred 'normally'
experienced advice welcome please..
