In my line of work I go on visits to many premises. Domestic, industrial, commercial, licensed and so on.
Something seems to have crept throughout local government in the last few years; the use of 'premise' as a singular for premises!
People who I otherwise like and respect seem to absolutely believe it is correct to say "I visited the premise"!
I once sat through an entire presentation on the Licensing Act 2003 where the speaker (a solicitor) insisted on saying "premise license" even though the powerpoint slides he was using said (correctly) 'premises licence'.
People who insist on using 'premise' are so convinced that they are correct I sometimes start to doubt myself.....