Rule good for top people with external connection (10)

'rule' is the definition.
(regulation is a kind of rule)

'good for top people with external connection' is the wordplay.
'good' becomes 'g' (abbreviation).
'for top people' becomes 'u' (upper-class, as in U and non-U language).
'with external' is an insertion indicator.
'connection' becomes 'relation' (I've seen this before).
'g'+'u'='gu'
'gu' placed into 'relation' is 'REGULATION'.