I have come across double pole fusing here once or twice I was told by an old electrician that they were from an old DC supply but had just been used when it was changed to AC I suppose it's possible that a few places in the UK had ,127/220 volt supply's I know central London had a 110 0 110 volt system it was AC I don't know the frequency.
I just found an old textbook from Austria that clearly states that in TT single-phase circuits it was still perfectly acceptable to fuse the neutral by 1972! The book also points out that fusing the neutral of a 3-phase supply or worse the PEN is a super-bad idea.
That explains the large number of fused neutrals in Vienna and the surrounding areas I'd say. Not sure when fused neutrals were eventually banned but my guess would be mid-80s or maybe even early 90s. In theory you're supposed to replace the neutral fuse with a solid link whenever you work on such an installation but nobody ever does - either nothing at all or the entire consumer unit is replaced. When we had our meter moved in 2003 the electrician connected the new supply to the old main fuses without as much as blinking so we still have a fused neutral ahead of the meter.
I do know people who got bit because they only unscrewed the neutral fuse, saw that the lights went out and thought the circuit was dead. Especially since very very few people bothered to label any fuses back in the day.
I wake this old thread. As far as I know Germany was pretty standardized to 220/380V Y 3-phase even before WWii.
An the other hand local standards has been surviving surprisingly many years.
Here in Norway we still have 230V 3-phase with no neutral. 3 wires with 230 V between and measured about 127 to ground until the first failure. Sometimes this results in a grounded phase and 230V between ground and the 2 others. On these systems we use 2 fuses, or more recent dual circuit breakers. Where we have 230/400V (newer) with a grounded center of the Y we still use double breakers, but not fuses. You shall not be able to switch off neutral without switching off live wires. This mix of systems makes the color-code of neutral wire confusing, because we use the same rolls of cables. Where Neutral is, it shall be blue, but when you have no neutral blue might be live wire. Actually no problem, always treat a wire as live!
Some of the very first 230V systems with neutral had fuses, but not on neutral. They even tried to use common neutral and ground to the receptacle, this is not by code anymore.
Any new supplies were 220/380 V 50 Hz by 1920 or so but older DC supplies and 127/220 V 50 Hz (TN-C or TT) survived much longer. In fact, there are still some 133/230 V systems (Y secondary but if there's a neutral supplied it's not used except as a PEN since there are no 133 V loads anywhere). In this case you have the same situation as in Norway - within the same city blue can be neutral or live at 133 V to earth.
TN-C with a jumper from earth to neutral in each socket and at each light fixture was fairly common in many European countries. West of the Iron Curtain it was generally banned for new work in the 1970s, on the eastern side much later. Eastern Germany had it until Aug. 1990, i.e. up to the point where the German Democratic Republic ceased to exist. In Western Germany it was banned in 1973, in Austria in 1976. In theory you can't even rent out an apartment with TN-C in Austria these days because the tenant protection law clearly states that newly-rented apartments must have all socket circuits protected by at least one 30 mA RCD but few people care (the law has been in effect for almost ten years and now landlords are slowly getting their heads around it - three years ago I was told by an electrician just to skip the required testing, no one would ever ask for the report!).
I think if ever I do any work in Europe the golden rule is test every conductor to earth just in case! We have a similar problem in the UK where the blue wire in a 3 phase circuit can be a live wire in old installations or neutral in new work of course blue is always neutral in single phase work.
Same situation here - grey used to be neutral, now it's a phase. Of course the transition took more time than in the UK because for almost 40 years grey wasn't really used at all (first round of harmonisation with abolition of grey neutrals in 1965, second round with grey L3 in 2003) but you can still find plenty of pre-1965 wiring. Heck, cities still have plenty of pre-WWII wiring and some pre-WWI just for the fun of it!
Every time an OAP passes away or moves you can expect to find mostly un-earthed sockets in the place (banned for new work in 1958).