If it's within a certain set of measurements, you don't need planning permission, and KT53 is right - the 'right to light' thing doesn't exist - urban myth. I think a structure of your own of some kind - an arbour with a seat, or just some simple trellis/screening on posts with climbers, would be your best bet. Painted a soft colour, it will help the offending, darker shed recede. I had a similar issue here as part of the neighbouring garage wall forms some of the boundary of my garden where the fence stops. I attached horizontal battens - to the fence at one side, and a post at the other - and put vertical planks on to match the rest of the fence. It's about a foot away from the garage and I have a small raised bed there and climbers on it.
The Beechgrove rope thingy was in a community garden ( can't remember where) not the one the programme is from. You'll get it on i-player I expect, if you don't have tv on demand to catch up.
It's a place where beautiful isn't enough of a word....
I live in west central Scotland - not where that photo is...
Deviating a bit but what happens in terms of right to enter to maintain, if both parties put things on the boundry line, one requiring no maintenence and the other neighbour couldn't get to do theirs ?
Not sure KEF. In my case, if my neighbour ever needed to do anything to the bit of garage wall my fence is in front of.... but she'd have needed access to my property anyway, even without the fence being there. Garage isn't painted, and the guttering is clear and accessible. I made the new fence lower - to match the rear fence rather than the one between us - as it would have caught the gutter. I'd obviously have no issue with anyone coming in to fix guttering if need be - there's no point in being difficult in these kind of situations. I expect someone will know the regs though.
It's a place where beautiful isn't enough of a word....
I live in west central Scotland - not where that photo is...
That's not a shed, its a log cabin. My neighbours have one at the bottom of their garden, about four feet from the boundary. We can't see it at all as both of us have plants screening it.
I would get an arbour, one with a latticed back to block out those windows and then you can grow all sorts of climbers over it, clematis, roses, jasmine, honeysuckle.
I wonder what's going to make their home under your neighbours one.
Thank you everyone for all your ideas and advice, great food for thought and I'll post any progress I really don't want to upset the neighbours as they are very nice and I know what it can be like to have nasty ones
And from some of your tales above we arnt so bad off
Garden maiden I think mice are already very much at home as seen one smiling at me through the wire vent bit!
Awww that's well nice of you to say and to be honest they hardly ever use the shed as think the hubby hoped for proper workshop but his wife has taken over with junk! Think a fence would need to be over 3 meters tall, and would look like prison wall
They are on hols now so we measured and it is over 3 meters high plus the base it's built on which they had to do to get a level.
Im dreaming of a barn type shed with tin roof I hope it will come half way across in front of theirs and then I'll screen off the rest of theirs then so should look pretty
Well I hope it does and probably a bit big of a dream according to my OH who will have to build for me
Posts
If it's within a certain set of measurements, you don't need planning permission, and KT53 is right - the 'right to light' thing doesn't exist - urban myth. I think a structure of your own of some kind - an arbour with a seat, or just some simple trellis/screening on posts with climbers, would be your best bet. Painted a soft colour, it will help the offending, darker shed recede. I had a similar issue here as part of the neighbouring garage wall forms some of the boundary of my garden where the fence stops. I attached horizontal battens - to the fence at one side, and a post at the other - and put vertical planks on to match the rest of the fence. It's about a foot away from the garage and I have a small raised bed there and climbers on it.
The Beechgrove rope thingy was in a community garden ( can't remember where) not the one the programme is from. You'll get it on i-player I expect, if you don't have tv on demand to catch up.
I live in west central Scotland - not where that photo is...
Deviating a bit but what happens in terms of right to enter to maintain, if both parties put things on the boundry line, one requiring no maintenence and the other neighbour couldn't get to do theirs ?
Not sure KEF. In my case, if my neighbour ever needed to do anything to the bit of garage wall my fence is in front of....
but she'd have needed access to my property anyway, even without the fence being there. Garage isn't painted, and the guttering is clear and accessible. I made the new fence lower - to match the rear fence rather than the one between us - as it would have caught the gutter. I'd obviously have no issue with anyone coming in to fix guttering if need be - there's no point in being difficult in these kind of situations. I expect someone will know the regs though.
I live in west central Scotland - not where that photo is...
That's not a shed, its a log cabin. My neighbours have one at the bottom of their garden, about four feet from the boundary. We can't see it at all as both of us have plants screening it.
I would get an arbour, one with a latticed back to block out those windows and then you can grow all sorts of climbers over it, clematis, roses, jasmine, honeysuckle.
I wonder what's going to make their home under your neighbours one.
Thank you everyone for all your ideas and advice, great food for thought and I'll post any progress
I really don't want to upset the neighbours as they are very nice and I know what it can be like to have nasty ones 
And from some of your tales above we arnt so bad off
Garden maiden I think mice are already very much at home as seen one smiling at me through the wire vent bit!
Thanks again everyone
Don't think they are allowed to build it ON the boundary, maybe wrong. Its awfully large
A neighbour had to take theirs down a few years ago because they put it in the front garden, council ordered it to be taken down.
I'd def put some sort of trellis up and grow clematis or something to block them looking in through the windows.
Hi star gaze, thank you for your ideas too, everyone has been great
Just need to plan the final plan and then rob a bank! 
Awww that's well nice of you to say and to be honest they hardly ever use the shed as think the hubby hoped for proper workshop but his wife has taken over with junk! Think a fence would need to be over 3 meters tall, and would look like prison wall
They are on hols now so we measured and it is over 3 meters high plus the base it's built on which they had to do to get a level.
Im dreaming of a barn type shed with tin roof
I hope it will come half way across in front of theirs and then I'll screen off the rest of theirs then so should look pretty 
Well I hope it does and probably a bit big of a dream according to my OH who will have to build for me