It was definitely 'in a peep' that Mum used to say, Malc. I Googled it and both are used, but "at" is more common. In my Google travels I found this wee poem:
Adam McNaughton: Folksinger, songwriter, Book-Dealer and Teacher
Oh, where is the Glasgow that I used to know,
Big Willie, wee Shooey. The Steamie, the Co.,
The shilpet wee bauchle, the glaiket big dreep,
The ba’ on the slates, an’ yer gas in a peep?
If ye scrape the veneer aff, are these things still there?
(Where is the Glasgow?)
I understand everything except for 'shilpet' - translation please!