If the verb ends with a vowel plus -l (as in travel or equal), then you need to double the l before adding -ed and -ing in British English. Oxford Dictionaries
Is it a general rule in British English? or there are some exceptions (feeling, kneeling ...)
In BrE you double the consonant only if the preceding vowel is short OR unstressed. In AmE you double the consonant only if the preceding vowel is short AND stressed. In both the consonant following a long vowel is single. "Feel" has a long vowel /fi:l/, so none of the doubling rules apply.
This rule mitigates problems caused by two other rules. 1) "silent e" at the end of a word changes a short vowel to a long vowel. 2) Appending "ing" to a word causes any "silent e" to be deleted. So how do you distinguish a short vowel from a long vowel before (consonant sound) + "ing"? The British English rule consistently uses doubling of the consonant after short vowels to make this distinction.
For words with unstressed vowels before -l, like "travel" or "equal", the doubling does not strictly depend on the dialect; many speakers write both "traveling" and "travelling" and consider them both correct.
answer transcribed from previous comments
