they are usually quite relaxed. so if you turn up without your ticket just explain the situation - take ID obvs
I got my son into a sold out game few weeks back. I've a blast pass and had intended to pay for him on the gate but was told it was sold out so I mentioned my mate (also a blast pass holder) who I usually go with was at home watching the Liverpool v Norwich game and wasn't turning up so they just printed me off his ticket and my son got in for free. Took my word for it. Wouldn't happen at the Albion - Barber would cringe at the laxness
Junior enjoyed the mauling of Middlesex and then collected a load of discarded £1 pint beakers for a bit of pocket money