Belgian,
I agree that in many cases reversing the brown and blue at the plug would have little or no effect on safety. You see the stickers attached to British cords about how essential it is that the wires are correctly connected though.
Many of the appliances sold in the U.K. these days are sold as the same model right across Europe. The two-prong "Euro" plug is non-polarized, as is the widely used Schuko plug (and a few others, e.g. in Italy). Even in France where grounding plugs are polarized, nobody seems too bothered about which way phase & neutral are connected at sockets.
The IEE is always quite adamant that all single-pole switches, even those inside equipment, should be in the "correct" side of the circuit.
There would be a case for some old electric heaters where the element terminations can be touched through the grill. If the switch were in the neutral, then somebody could touch an energized terminal believing the heater to be safe. But they don't allow those to be manfactured these days anyway.
The only other case I can think of is where a primary fuse is included on the supply input (typical of some radios, TVs etc.) and reversal could remove the protection by having that fuse end up in the neutral. It would still provide overcurrent protection, but not protect against ground faults.
Perhaps with the prevelance of TN-S and TN-C-S systems in Britain this was a major concern, whereas so much of residential service in Europe is TT where the main GFI/RCD would provide ground-fault protection. (As would also apply increasingly in this country.)
