Socialised in hotel with old pupil, toff and qualified teacher (9)
I believe the answer is:
hobnobbed
'socialised' is the definition.
(I've seen this before)
'hotel with old pupil toff and qualified teacher' is the wordplay.
'hotel' becomes 'h' (phonetic alphabet: alpha, bravo, charlie etc.).
'with old pupil' becomes 'ob' (I am not sure about this - if you are sure you should believe this answer much more).
'toff' becomes 'nob' (UK slang for a wealthy or upper-class person).
'and' is a charade indicator (letters next to each other).
'qualified teacher' becomes 'BEd' (someone with a Bachelor of Education degree).
'h'+'ob'+'nob'+'bed'='HOBNOBBED'
'in' acts as a link.
Can you help me to learn more?
(Another definition for hobnobbed that I've seen is " Spent time together, socialised".)