Plot hole: Mickey Bricks returns to England by stealing the uniform of a Commander Cardwell, an officer in the Royal Navy, and taking his place on board an aircraft carrier that is sailing from Australia to the UK, leaving that day, a voyage that would take three to four weeks. During that time, Cardwell does not report his uniform stolen, nor does he report to the aircraft carrier to take up his duties, and since there was a car waiting to take him to the ship he is obviously supposed to be there. Theft of a military uniform is taken extremely seriously and once reported it would take no time at all to establish that "Cardwell" appears to be on board his ship! On top of that, during his entire time at sea nobody on board calls upon Mickey to perform any sort of military duties (of which he would have absolutely no knowledge), he doesn't run into anyone who knows Cardwell, and nobody asks to see his orders, military identification or travel warrant.
Plot hole: The only people who respond to Harry Fielding's classified ad seeking victims of the gang are three people who, it turns out, are actually working with Mickey Bricks. Considering how prolific the grifters are I rather think Fielding would be inundated with genuine people seeking revenge, but not one shows up. Not one? Simply unbelievable.
Plot hole: When Albert, Mickey and Emma are trying to decide which nationality of millionaire Albert will pose as, they decide not to go with an English millionaire, since Albert at this point tries and fails to do a remotely convincing upper-class English accent. However, in many earlier episodes (such as "Gold Mine") he has no problems at all in putting on a convincing upper-class English accent.