What's the finish as I cannot tell from your closeup?

Most suppliers offer a touch up paint. Less is more here and apply with a model details brush once the scratch is clean.

It's a normal white aluminium window. I'm not sure exactly what kind of coating covers the aluminium, I assume it's some kind of plastic finish?? I did come across a product for upvc windows on Amazon https://www.amazon.co.uk/White-Konig-Scratch-Repair-Touch/dp/B00MJ1BMRS/ref=sr_1_1?ie=UTF8&qid=1488268518&sr=8-1&keywords=scratch+repair+upvc. Do you think this would solve the problem for an aluminium window? Hopefully this thread will help others with similar issues. Thanks

Is the scratch in the window or in the trim cladding on the exterior? Most window, if when aluminum clad, will not have a PVC texture on the exterior. How about a picture from further back?

ok, great! So an enamel gloss paint suitable for metallic surfaces should do the trick?

Should work fine. As suggested before, I would contact the manufacturer and see if they will just send you some touch up paint. Most will.

If you have the mfr go to a BM or a SW dealer with the paint color name or a color chip if you have one. Have them mix a quart and buy a few model brushes. Many if not most mfrs offer touch up paint which will probably be an aerosol but you can spray a small puddle onto a pc of cardboard and use the same model brush technique.

Thanks for all the advice!