I've been meaning to fix this scratch, what is the best way?

I've purchased a ford touch up kit from eBay but not sure how to use it! 

I'd try T-cut first, touch up will probably make it look worse.

Does your fingernail get caught on it? That's means it's a deep scratch gone through the laquer and probably base coat. T-cut (or any other modern polish that performs a lot better than t-cut) wont fix that no matter how hard you try.

Touching up silver paint is quite hard, but I've always just used a tiny brush (for arts/crafts) and a borrowed a tiny amount of paint from my local sprayer (good friend of mine). The key is to build up many layers over time rather than build the paint up in one go. Do the latter and you'll find yourself wet sanding to get it flat and will take off too much paint from the surrounding area.

22 minutes ago, Luke4efc said:

Does your fingernail get caught on it? That's means it's a deep scratch gone through the laquer and probably base coat. T-cut (or any other modern polish that performs a lot better than t-cut) wont fix that no matter how hard you try.

Touching up silver paint is quite hard, but I've always just used a tiny brush (for arts/crafts) and a borrowed a tiny amount of paint from my local sprayer (good friend of mine). The key is to build up many layers over time rather than build the paint up in one go. Do the latter and you'll find yourself wet sanding to get it flat and will take off too much paint from the surrounding area.

I believe my fingernail does get caught in it, it's quite deep. 

I was thinking of taping up the area around it, even using newspaper to cover the area around the scratch then attempt the painting.

I will use a small brush then or a toothpick and build up the paint as you mentioned!

If I screw it up can I fix it? 

It's not easy. If it's deep a high build primer would be good to fill the void the touch up pens are rubbish. Then for the top coat you get great stuff on eBay that has the shine in it already so no need for laquer. A wet sand slightly afterwards to blend and then compound to remove the scratches then polish.

Primer:   https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F351914124537

Top coat: https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F390688441296

Compound: https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F121666237997

Polish:: https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F163077777553

9 hours ago, Luke4efc said:

Does your fingernail get caught on it? That's means it's a deep scratch gone through the laquer and probably base coat. T-cut (or any other modern polish that performs a lot better than t-cut) wont fix that no matter how hard you try.

Touching up silver paint is quite hard, but I've always just used a tiny brush (for arts/crafts) and a borrowed a tiny amount of paint from my local sprayer (good friend of mine). The key is to build up many layers over time rather than build the paint up in one go. Do the latter and you'll find yourself wet sanding to get it flat and will take off too much paint from the surrounding area.

I did wonder, tried it without success on my last car (Fusion), i just put up with it in the end. 

 

It's one of those things where it will probably end up looking worse after you attempted it and you might wish you have never tried. If this was my car I would T-cut it which often makes it look slightly better (but not always) and then leave it - unless I can actually see bare metal in the bottom of the scratch. if there is bare metal the rust will start, so I would carefully brush paint into the scratch with the finest brush I can find (something like a small brush you would get in a young child's painting set). That woud not make it look any better but it would be preventative to stop the rust which would make it look much worse over time.

So many times I see attempted repairs on car paint which look worse than if it had just been left as it was

If you do have a go please show us a photo of the result

I have a couple on mines as soon as I have all the materials, I have all apart from the top coat I'll do a before an after.