Foundation CS to higher ranking uni

Is it possible granted i get very high on my modules to transfer to a high ranking university like top 20? I didn’t take the right a levels for CS course so i have a foundation year, from this can i transfer to a better university?

Foundation years aren’t transferable - they’re designed to prepare you for year 1 at the university teaching them not for any university first year.
If you don’t have suitable A levels then you’re generally better off either looking for foundation years at the universities you want to attend for your entire degree or taking 2 fast track A levels in a year to apply for first year entry.

What if i enroll to a 3 year course without a foundation year? Could i transfer after year 1?

You could apply for a transfer to restart year 1 elsewhere - some universities will accept year 1 study elsewhere as a supplement to lower A level results.
Generally to transfer into year 2 you need to meet the entry criteria for year 1 entry AND do well in year 1 AND have a very close similarity on learning outcomes of the year 1 modules for the 2 courses. Which means it isn't normally an option to bypass the standard entry requirements.