Ah shit.
My coin sorting/counting machine is probably going to think some of the new £1 coins are 10p's because it sorts them by their diameter, smallest first so a £1 that doesn't fit in the gap will then slide along and fall through the 10p gap, screwing up the counting result.
£1 = 22.5mm diameter
10p = 24.5mm diameter
New £1 coin = 22.5mm to 24.5mm diameter
Time to drop the machine back on eBay before everyone gets wise...