Hardly / Scarcely  :  This usage shows how quickly two actions take place.  The second action takes place immediately on or after the first action takes place.  We can combine two sentences using  ‘Hardly ‘ or ‘ Scarcely’ .  Normally ‘ Hardly’ or  ‘ Scarcely’ is used at the beginning of the sentence.  When the two sentences are in the simple past, the first sentence is converted into past perfect and the tense of the second sentence is left unchanged on combining the sentences.  Words such as ‘ suddenly’ , immediately, soon, then etc which may come at the beginning of the second sentence should be omitted and ‘WHEN’ should be used in such places when combined.  ‘Hardly ‘ and ‘Scarcely’ are negative expressions and therefore when a sentence begins with a negative word, inversion of the subject and auxiliary is a must. This usage is a little bit of a difficult expression and as such this may be avoided in spoken as well as written English.  Instead , you can use ‘ As soon as ‘ expression conveniently to replace it.( Example:  As soon as the police resorted to lathicharge, the people scattered here and there. All the following sentences can be combined using ‘ As soon as ‘ Expression conveniently.

• The police resorted to lathicharge .  At once the people scattered here and there.
• Hardly ( or scarcely) had the police resorted to lathicharge when the people scattered here and there. (combined)
• The students were waiting for the school bus and at last it came.  Then they rushed to it immediately.
• Scarcely ( or hardly) had the school bus come when the students rushed to it. (combined)
• The thief saw the police officer.  Suddenly he ran off.
• Hardly (or scarcely) had the thief seen the police officer when he ran off. (combined)
• We reached home.  It began to rain immediately.
• Hardly (or scarcely) had we reached home when it began to rain.(combined)
• I saw him.  At once I stopped the car.
• Hardly (or scarcely) had I seen him when I stopped the car.