The episode set in London (supposedly)

I think it would have too expensive and impractical to shoot in England to avoid all the nit-picky things and the producers figured that the mainly American audience wouldn't pick up on the incorrect shopping bag and accents--after all we think all Aussies sound like the late crocodile hunter, Steve Irwin. Most aren't attuned to the various English accents, and face it, American accents run the gamut too--from the New Jersey housewife to the Southern good old boy.

The errors you point out about the license plates and shopping bag fall more to the props department than the writing. Scripts don't get specific like that. They'll say:

EXT. LONDON - STREET IN HIGH END SHOPPING DISTRICT - DAY

Did the props department do a bang up job? No. Kinda like the setting for the Conduit episode. A simple Google Earth search would show Mack could not have been in Cartagena. Those things can annoy you if you know the area, or that the Army doesn't fly the kind of aircraft that the studio can afford to buy and use for the show, but it's the big picture things that hurt the show worse than this. Can you say "Spear of Destiny." The lack of Mack minutes in Side Angle Slide was a greater travesty than the incorrect shopping bag.

http://www.booksforsoldiers.com

And in one of the scenes I saw a classic Volvo parked in the street. The same one used in a season 2 episode with the competition between all the units from different countries (with the subway threat).

But hey, that really is the props department, and all things considered, I think they did a great job giving each episode a good feel of the area they're in. Of course you don't see too many surroundings, when you see a wide shot it often is an industrial zone or snow peaked mountains are edited in.

But I only saw those things since I watched the show a second/third time. Then I paid more attention to those details.

They never invested much money and research into the episodes abroad, I think. Of course, Americans who have not been to the particular spot, wouldn't notice. Locals would: The Hamburg, Germany, episode being a point in case for me.

Just what I noticed while watching: Wrong architecture (French), wrong fire hydrants (Parisian), wrong number plates (yellow, end "75", uh... Paris? ). I think they found a disused "Paris" set on the lot. Wrong underground trains, wrong names for the Germans (about 30 to 40 years out of fashion, they've been watching too many war movies ).
Also, GSG 9 is a police unit, and rarely runs around in James Bond outfit (it's uniform or normal civvies).

A thing they got right was the signage around the set --the texts were faultless and grammatically correct German, and the underground system used a mock-up of the real HVV maps and signage (as "VHH", IIRC). In real life an icon instead of a text would have been used in some cases, though. For example, we don't have text signs telling people there is a lift for wheelchair users, we use an icon. Oh, and the taxis were the correct colour and had the correct Taxi bar on top.
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"I only watch box sets. Soya latte anyone?" (GuardianOnline reader CameronYJ)

First thing I noticed was the MI6 building with the caption MI5. How hard is it to get something like that right?