Hi, in answer to all suggesting applying to the DVLA for a duplicate licence and then giving it to the Spanish Authorities for an exchange is not advisable as licences are security coded ,and the last licence applied for is THE ONLY ONE VALID on the DVLA system, and any other licence copy will be cancelled on the system. so if your duplicate turns up anywhere, which it almost certainly will, and the Spanish will check the licence given is valid in the UK, then you may find yourself on the end of some VERY awkward questions from the Spanish , AND English authorities, and most likely prosecution for fraud also. Also the other licence in your possesion if its the new one will also be cancelled by the DVLA once the Spanish confirm the licence application in Spain, so basically, forget it.
Also the licence downgrading from 7.5 tonne to 3.5 tonne is done as the spanish are giving you the licence entitlement in the EU for a normal car licence, which the entitlement is the same post 1997 in the UK, the 7.5 tonne entitlement being an outmoded UK entitlement, only allowed as "grandfathers rights" to pre 1997 licence holders, and only valid in the UK
Hope this clarifies things, Rob