you can only use primer if it remains below the paint surface, i.e. the primer does not completely fill the scratch. if it does fill the scratch, once smoothed it will always show the primer. you need a very deep scratch to use primer (galvanised coating removed type scratch).
i would only use touch up paint. get it as level as possible. then let it dry for a couple of days. once dry you can use original t-cut and a rag wrapped around something flat (e.g. bit of wood) to smooth it down. if you rub back and forth across the scratch in circular motions (done both ways gently) you'll slowly remove the touch up paint until eventually you get to the point where the surface is smooth and the touch up paint is only inside the scratch. thats the first stage. its not as easy as it sounds. you dont want to remove any of the original paint if you can help it, so be gentle, fresh touch up is surprisingly easy to flatten, but it takes time, not force.
once flat let it dry again for a day.
you'll notice loads of tiny scratches around the area you used original t-cut on. to get rid of them use colour t-cut and a polishing cloth. gently rub over the area to remove light scratches and give a better finish. do not try to remove any paint, just buff the minor imperfections out. this will usually also improve the colour match.
once you're happy with the surface, apply some good quality carnauba wax. this will keep the area shiney for many months, removing the need for laquer and making the surface finish better. if you smoothed the touch up paint correctly the scratch will now be difficult to notice from most angles.
end of the day, it will never be perfect, but a smooth surface and good colour match will make the scratches practically unnoticable.
halfords paint is almost always much darker than the actual paint colour (but surprisingly cheap!), thats why you should use the stuff from your dealer.