The L at the end of “feel” is always pronounced in all standard accents of English. In American, it’s usually pronounced “dark” (velarized, a bit like final -ng), with a glide into a semivocalic schwa before the L (as in Beijing Mandarin in the -ing final). It may perhaps be pronounced more as a light L in some other accents if the following word starts in a vowel. What exactly do you mean by in the UK? Setting aside Wales, Scotland, and Northern Ireland, England has a shocking number of different accents. In Cockney, the final L is often pronounced /w/, if I’m not mistaken. I’m not aware of any accent that would pronounce “feel” as “fee”, but who knows, there may be one somewhere in the UK.