Ok so got home and found 2 letters which look suspiciously like NIP letters from the police but they aren't addressed to me or the misses but to a Mr Jay Smith.

Scam or has someone used our address somewhere?

If there is a return address on the envelope then simply write return to sender, not known at this address.

Yeah that's what I was going to do. going call the number I have found too just to check. Just wonder how they got my address as I thought they normally get sent to the v5 address....

Jay smith is pretty suspect as name lol.

Short answer
As above ^^^

My two penneth of experience (not specific to NIP but..)
I've had issues with a previous house owner leaving bad debt and repeatedly sending them back to the return address did the trick eventually although it probably took a couple of years for them to stop coming.
My folks have had this issue for years from someone who managed to get credit from their address (someone who they know had never lived there) and the debt company it ended up with just churns out letters forever it seems. The bank who the debt was with originally gave them £200 compensation for the inconvenience a while back but the letters keep coming (with sod all tangible action on behalf of the debt collectors).

You touch on my concern Wishy. If someone has used my address what else are they using it for? If there is something on record at the DVLA or with the police I want to nip it in the bud so to speak.

Legalities of opening up someone else's mail aside (IANAL), you could always open one and find out what you are dealing with, especially if you end up with more than one of the same thing (as in send the first back as "not known" and open the second). I think I kept a record of what I was getting so I knew when it was something from the same company. This way you've sent an anonymous "not here" response and they (the man/debt collection company/entity that will prosecute you for opening mail that wasn't addressed to you) have no way of knowing that you haven't done the same with second and it possibly just got lost in the post.

Probably need some proper legal person's confirmation here but as far as I understand the law changed a while ago so that a debt can't be held to an address just a person (edited to add: or registered keeper in the case of NIPs but there are differences between the types of liability).

Might be worth popping in to your local police station, with the letters and explaining.

They will probaby be allowed to open the letters and they might get the problem resolved there and then for you

NIP are issued to comply with the requirements of S1 of the Road traffic Offenders Act 1988. from the sounds of things the letter is not addressed you, but delivered to your address. In law certain offences must be brought to the attention of a driver before prosecution. There may be a number of reasons it has been sent to your address (assuming it is an NIP letter) ranging from the offender 'twirling' an officer on the roadside to not updating DVLA when a vehicle is sold. Either way it is not going to incur a debt for you or a charge to be registered against your property so just return to sender marked not living at this address. End of.

I had to look this up, and discovered an unexpectedly fruity definition in Urban Dictionary

aka giving duff details

Ah.....not so colourful, but perhaps more acceptable