if the flight is full and everyone brings the max, no chance they fit and start enforcing... depends on route and time of year... never seen them check at all on domestic.
Well they are now. Seen it twice now on the LBA-NQY route. And people being forced to pay £50 to check bags into the hold when they don't fit. And their frames are very strict on the dimensions -- my other half's small suitcase at 20cm deep had to be rammed in and tugged out to fit..