Can anyone help please if I add honey at the bottling stage will this add more sweetness and what sweeteners are non fermentable?
Honey is almost 100% fermentable, so if added at bottling, it can increase carbonation and potentially result in gushing overcarbonated bottles or even explosions. You can however use it to prime the bottles instead of sugar. In proper amounts you will get normal carbonation. I have used honey one time as priming sugar and it worked well, however I forget the amount that I used. There are online calculators that can help with this, perhaps try this one: https://www.northernbrewer.com/pages/priming-sugar-calculator
A better alternative for sweetening that is used often by brewers is lactose. This sugar is not fermentable and will also increase body and mouthfeel of the finished beer. Assuming 5 gallons (19 litres) of homebrew, if you use 1/2 lb (~225 grams) it will add just a hint of sweetness and body, 3/4 lb (~340 grams) adds a good balance of sweetness without being overpowering, and 1 full pound (~455 grams) adds significant sweetness and body that will be most noticeable in the finished beer.
Lactose is difficult to dissolve and must be boiled in a little water for several minutes until no longer cloudy and well sanitized. Then cool and add to the beer. I do this on the same day as bottling with excellent results.
I have also tried xylitol on a few occasions. This is another non-fermentable sugar substitute. It is a natural sweetener that comes from the birch tree. I use it for my ciders but it will also work in beer. It works in much the same way as lactose and can be used in the same amounts. It is cleaner tasting than lactose, and it does NOT have a chemical taste the way you might get from Splenda, aspartame, stevia, or other sweeteners, which I have also tried but are nowhere near as delicious as xylitol or lactose.
You can adjust the sweetness in two other ways not already mentioned.
Through adjusting the mash temperature and time. This will affect how much the natural starches are broken down. Generally mashing at a higher temperature will yield a less fermentable wort and could lead to a "sweeter" tasting beer. This sweetness would be a malty sweetness.
Using a high percentage of caramel or crystal malts in the grist. These contribute to sugary flavors in the finished beer. High percentage with these is relative. Too much can be cloying.
There are several ways you could go about trying to make a sweet beer.
Honey will of course add sweetness, but only if the yeast do not ferment it away in the bottle. (Which will also cause the bottles to explode, if you add too much of it.)
As for non-fermentable sugars, I found the following list on https://www.homecidermaking.com/non-fermentable-sugar-for-hard-cider/
Of those, I know that maltodextrin can be produced naturally during the malting process, and is found in certain specialty grains. Typically it has no flavor, but provides a texture of 'fullness'. You can also buy it as a powder, and some varieties have a perceptible sweetness.
If you are using a keg, you also have the option to kill off the yeast with campden or by heat pasteurizing. Once the yeast are out of the picture, you can add however much sweetener you want, and then force carbonate in your keg.