Although the regulations say 3 and 5% volt drop careful selection of items can allow a far greater volt drop without a problem. ... This guy has a problem and thinking outside of the BS7671 box there are ways around the problem.
In fact, one doesn't really have to think outside of the BS7671 box. The 3% and 5% figures are merely those which are 'deemed to satisfy' the VD requirements (i.e. for those who don't want to think). However, the regs are also satisfied if the voltage delivered to the equipment is at least as high as the minimum voltage specified by a relevant product standard or, in the absence of such a product standard (which will most often be the case), a voltage adequate 'to not impair the safe functioning of the equipment'. It doesn't even say 'satisfactory functioning', merely 'safe functioning'. Hence, as you suggest, VDs considerably in excess of the default 3% are likely to be acceptable (and compliant) for many lighting loads. The default 5% (for everything else, including sockets circuits) is perhaps more difficult to get around- whilst one could confirm that greater VDs did not impair the 'safe functioning' of fixed-wired loads, one could not really do so for sockets circuits, since one would not know what might be plugged into them.
In any event, the BS7671 default figures are perhaps a bit naive in talking about VD rather than delivered voltage. A VD of 3% or 5% from a supply voltage of 216.2V is (in terms of voltage delivered to the load) clearly a very different kettle of fish from a VD of 3% or 5% from a supply voltage of 253V. I suppose the implication has to be that they believe that all lighting loads will work satisfactorily with voltages as low as 209.7V and all other loads will work satisfactorily with voltages as low as 194.6V - which I'm far from convinced would always be the case. The BS7671 defaults may therefore, on occasions, 'fail' in both directions.
In reality (although I realise that this could theoretically change 'overnight') many of us, like me, are in the position that are supply voltage is never even as low as 240V. So long as that remains the case, I could have VD of at least 13% before the voltage delivered to the lights fell below that in the 'worst case' of BS7671's default 3%.
I have to say that, in 'common sense' (rather than regulatory) terms, VD is usually the aspect of circuit design which least concerns me (but don't tell anyone that I said that!).
Kind Regards, John