Okay.
I'll tell you what I was thinking but it's probably not so relevant if their main entrance/exit is not on that lane.
In a dispute like this there is usually a small trigger that sets off the escalating issue. Like an emotional avalanche it would have got going with a very small drip of something seemingly inconsequential. What fuels the issue along at increasing speed ceases to be the original trigger and becomes something in its own right... a perpetual motion juggernaut of contempt that has long since forgotten the small thing that got it rolling to begin with.
The problem with us - all of us - is that in a dispute we harden up and refuse to consider the opposition's position, their perspective or feelings. To do so would seem to be weakening, and it's just human nature to hunker down and entrench behind a perceived line of defence. Most conflicts are very easily resolved once both sides are able to relax enough to see the other person's point of view. It doesn't mean you have to agree with it, but it's really helpful to understand it because understanding what the real problem is beneath the tornado of invective and emotion often reveals a very simple trick to disable and neutralise the entire dispute.
So I was thinking in this case, maybe the situation beneath all of the curse word they're flinging at you is something simple, such as (scenario modelling follows, entirely hypothetical I have NO idea whether it's even remotely correct or not, obviously)
Maybe they've lived in their house longer than you've lived in yours. People always apportion significance to this. If they were there first, any changes you have made to their life since you arrived (however small and insignificant they might seem to you) will have an emotional effect on them. Life before GrumpyNortherner was one way, now life since GrumpyNortherner arrived has changed. They will resent you for those changes.
They lived a peaceful life in their idyllic country cottage on it's own private land. Peaceful, relaxing, pastoral, rural... maybe a retirement utopia for them.
Grumpy Northerner comes along. maybe... MAYBE... you didn't match their ideas of courtesy and politeness. Maybe they felt snubbed by you on day one for some small reason you didn't even register. They felt they were pleasant, but you seemed gruff and surly. In a small way maybe this alarmed them a little. The arrival of somebody new who in some imperceptibly small way has rippled their happy existence. So they're on their guard now. feeling edgy about change. People really hate change.
Next thing they know there's a planning application for what to them could potentially be a greasy mechanic's hell hole. Their imaginations envisage a day six months after planning approval is passed that you're out there with an angle grinder chopping Ford Sierras in half, filling the lane with old oil and coolant, stacking up car batteries and old wheels, flicking fag nubs over the hedge and swearing your head off as your greaser buddies rev the nuts out of a pimped up Beemer. Hell on earth for them. They're terrified of this potential future. So they do what everybody always does when they see a planning application. They panic, they resist, and try to block it. It becomes their fight. A fight to protect their idyllic pre-GN existence. How could you come along and destroy their happiness like this?
They wont let you! Their entire lifestyle is on the line here! PANIC STATIONS!
But they lose. You get your planning approved.
By that point, they are already fully jacked up on animosity, resentment, hate, fear, paranoia, angst and stress. They cannot comprehend the notion that you might actually be considerate, sensitive to the environment, focussed on the careful restoration of vintage vehicles. Any attempt you make to assure them of that will just be seen as a ruse to lull them into complacency. They are still trying to protect an endangered tranquility that was not threatened before you arrived. They can't relax about it because you're right across the lane EVERY SINGLE DAY and LOOK! LOOK MAUREEN! HE'S GOT ONE OF THE THOSE AUDI TP HOTRODSTERS OUT THERE NOW! THAT'S NOT A CLASSIC CAR! OH GOD IT'S STARTED MAUREEN! HE'S BRINGING HOTROD HELL TO OUR HAPPINESS! I NEED MY PILLS!
By THAT point they are just freewheeling on their own fears, and have lost objectivity. They hold fast to an emic perspective. They cannot translate the objective view to assuage the subjective fears they are now consumed by.
Fear of a commercial enterprise not 20 feet from their tranquil oasis will amplify the impact of every single signifier of business activity they are exposed to, however small. They may not be trying to be deliberately aggressive and heavy handed with you in terms of the complaints they make. They may well be genuinely seeing small signifiers of your work as huge monstrous threats directly over their hedge in the lane right outside. A car engine noise (HE'S REVVING THAT RACE CAR AGAIN MAUREEN!), the clanking of a trailer (HE'S SMASHING UP A BANGER MAUREEN!), the hum of a compressor or air filtration system (HE'S OPERATING INDUSTRIAL MACHINERY AND FILLING THE AIR WITH RADIOACTIVE ASBESTOS AGAIN MAUREEN!). The sound of a drill, the clank of a ball peen hammer on sheet metal. The aggressive THUD as you put your tea cup down on the workbench... It's all amplified by their constant stress and fear. It all becomes Life After GN and life before GN never had any of these problems.
The entirely decorative, period correct and very charming signs attached to your workshop exterior are, to their fearful eyes, exactly what they are... commercial advertisements. That monster has started putting advertising materials on the outside of his workshop!. Right outside our house Maureen! We don't want a commercial premises with commercial signage all over it outside out house! He's turning this once peaceful enclave into a trading estate! IT'S ONLY A MATTER OF TIME BEFORE THE HELLS ANGELS TURN UP MAUREEN! All you see is vintage charm. All they see are advertisements. We don't all appreciate the same things.
To your mind, and to everybody's minds here, the conclusion is they're just bitter hateful people with nothing better to do than to try and cause you distress and make you anxious. What if they are actually just very scared about threats to the peaceful life they crafted here before you came, and not knowing what to do about it what if they are just hammering away at attacking whatever triggers them next in whatever way they can. What if they are actually driven by an anxiety that they are now transposing onto you, making you feel the same anxiety? What if for the next 20 years the two households spend their entire time zapping each other with anxiety like cold war enemies who refuse to talk the same language. You don't want that, and I'm sure they don't actually want that either even though they are currently driving it.
For them this is all a self-fulfilling prophecy. This is life under the shadow of GN and his Punk Rocker Banger Racing Factory. Daily angst and stress. A total lack of any calmness and tranquility. Subconsciously they are actually self-actualising their worst nightmare. You actually are the enemy, and their erratic acts of aggression towards you are bizarrely the very things that inflict emotional damage on them, which bizarrely they will then blame you for. It's a horrible spiral into a miserable future for both parties. The truth is, however you look at it... life has got a lot more stressful for them since you arrived. Sure, they're smacking themselves in the face but still YOU DID THIS! YOU DESTROYED US! MAUREEN HASN'T SLEPT IN MONTHS FOR WORRY!
Before things get any further... and with these things there's generally no going back once it's escalated pst a certain point... what if you were to be the better person and along with your wife you invite them over to yours for a cup of tea and a frank discussion, and you make them feel comfortable enough to air their thoughts which you listen to carefully and sympathetically without interrupting them or refuting what they say. Then you can all talk through it all and AFTER they have said their bit you can reassure them that you are never going to lean half a burning Renault 14 up the hedgerow or spend your Sundays tuning up a home built drag racer while listening to Black Sabbath. Once people have looked each other in the eye, and shared a cup of tea, and shown each other sympathy and sensitivity, it usually all just melts away.
As impossible as it might seem at this point now, the simple act of telling them you understand their concerns, and you have no desire at all to upset their existence with anything more than one car at a time in your workshop, behind closed doors... and maybe even though you don't have to do it at all you could offer to remove the exterior (decorative) signs and the security camera.... maybe this whole thing goes away and you all feel a huge sense of relief that this bizarre war of attrition is finally over.
It's very easy to only see one side and condemn that side as being something or other, but I'm convinced... absolutely convinced... that neither party wants this to be the defining feature of their life. They're not enjoying this any more than you are believe it or not. They'd give anything to go back to how life was before this self-inflicted conflict emerged, I'm sure of that. They just don't know how to stop now because they are entirely under the control of their own fear and panic.