香港人英國運毒在當地被判監, 會否留有香港案底?

1. 係英國坐監, 會唔會影響係香港申請良民證?

No, HK CNCC will only list the criminal activities of a person in HK, but, it will state the record ended 3 years ago, when the requesting authority sees it, they will ask for the 3 years gap and have your friend to supply panel clearence of those 3 years,so it will end up the same.

2. 佢下次去英國會唔會比較麻煩? 係咪唔可以免簽證進入英國? 入其他歐盟國家會唔會有麻煩?

Your friend would not be admitted to UK anymore (Visa or no visa), he should be deported because of the criminal activities, he will have a record in UK and he will be refuse entry in any UK border entry port.

Depends on which EU country you are talking, most have linked system with UK, so when you are refused entry from UK, you would be refused else where in EU.