How might the proposed changes to UK mains voltage limits affect older electrical infrastructure?

Well currently the voltage can be anywhere from 216 to 253, and the proposal is only to declare the 5% below (207 to 216 ) as no longer out of spec. The intention is to allow it to droop a bit more when EVs are charging and maybe set the taps one click lower so it has the freedom to surge a bit more without going out of limits on sites where that is an issue when embedded generation kicks in.
In some ways actually this proposal is only acknowledgement of what is already happening...

I will be very surprised if DNOs rush around shifting any transformer settings except where there are persistent reports/ complaints of things being too low or too high, and this really allows them to say they don't need to do so just yet in a few edge cases.

If you don't already have voltage problems, I suspect you won't see any changes at all, until additional solar panels or EV chargers are added at your site, and then only if the additions force a change of transformer configurations.

At that point whole site step up or step down may be worth a look, but very few things are that critical.

If as it sounds, you are the only load on the transformer, then it is not uncommon to ask the DNO to set it a bit high or a bit low as your local needs require, and normally they can oblige. (typically 2.5% steps )

Mike

In terms of effects, transformers run a bit cooler and buzz less, and motors take longer to spin up. Anything with feedback to control its speed will still level off to the same value, unless it was already at its upper limit, but may well take longer to get there. You may find that as voltage drops, the fault current reduces and the operation of breakers and fuses gets slower - not so much an issue if a fuse takes 6 seconds instead of 5, but a breaker that is supposed to fast trip , may not fast trip if the circuit impedance is marginal, on a low voltage day. If this really matters is often hard to tell - quite often, especially in cases with RCBOs and earth fault relays, it really does not, as the breaker part is only protecting cables from overload and overheating effects, while the fast safety of life is handled by the RCD part which is always fast.
Mike.

Thankyou Mike, Thankyou for taking the time to reply.

Do check back in a day or two, I'm sure others will also have an opinion ;-) 
Mike.

PS In the past I have seen problems with persistent low voltages and an alarm  panel and emergency lights not recharging fully, where lead acid cells were involved and the charger was a simple unregulated transformer and rectifier set. More modern ones have regulated supplies and proper battery management to 13.8V float, and then its not an issue. And lead acid cells are not the only type used these days so makers and installers are a bit more aware.

Interesting - I hadn't heard of the recent proposed changes before.

From what I can gather the proposal is to move from 230V +10% / -6% to 230V +10% / -10% ... i.e. what my 16th Ed brown book says was originally proposed for 1st January 2008! (but then later dropped).

I think the idea then was to bring us fully into line with ex-220V lands - as their change to the tolerance bands was initially the opposite way around to us (something like 230V +6% / -10%) - so we'd eventually meet up at +/- 10% for all. I believe it was the filament lamps the scuppered that plan though - the simple tungsten technology couldn't cope with such a wide voltage range - resulting in either obviously dim lamps or unacceptable reduction in service life, so even after 230V harmonization lamp manufacturers still produced separate 220V and 240V versions.

These days though, the filament lamp is just about extinct, so problems should be fewer...

   - Andy.

As with lots of things the answer is it depends.  EG. 6amp rcbo trip time at 207v vs 230v vs 240v vs 253v 

The primary effect of different voltages relates to the current that can flow for a given fault or load (Ohm's Law: \(I=V/R\)). A lower voltage (207V) will result in a slightly lower current than a higher voltage (240V) for the exact same circuit resistance: For any given current level above 6A, the trip time is determined by the fixed trip curve (eg Type B or Type C).The only practical difference is that a specific fault resistance might draw a slightly lower current at 207V compared to 240V, potentially moving the fault to a different point on the time-current curve and resulting in a marginally different—perhaps slightly longer—trip time

The above being said a pump or a motor at the low end of the voltage spectrum might start to seem underpowered or run slower which could be an issue for some that have the pump set to a run time rather than a volume or sensor on and sensor off.

Caveat time.

240v in the UK became 230v nominal ages ago.  (about 1994) but in Yorkshire (other regions are available) 250v and above are quite regular.  The DNO/DSO/NG are probably in no rush to change the transformer tap to 207v but they reserve to use the right of 207v IF it is needed espcially for single phase.  This is probably being lead by the amount of re-newable energy be ProSumed/Generated

Its also worth noting that it would be a most odd situation where you saw the full variation from 253 off load to 207 on load, partly due to the heat losses in cables becoming more than 20% of that in  the load, and partly because you would have problems to arrange circuit protection safely. A consequence of  droop of 20% under  load is that the PSSC is only 5 times the full load current -  and given that most fuses will carry 100% overload i.e. 200% of nominal rating, for ages, and at a multiple of less than 5 times a B type breaker may not prompt trip and a C type is guaranteed by design, not to, then unusual measures (well earth fault relays and shunt trips) are needed. Also by the time you add on the permitted voltage drop in the final installation the socket in the garage at the end of the garden in the house at the end of the street main is looking very poorly ;-) 
You would only really expect to see both extremes when at some time of day local generation reverses the slope of the voltage drop, and then at other times heavy loads take the full quota.
I'd expect this concession to be used by the DNOs as a reason not to adjust things, rather than as a basis for re-setting transformers where no problems are reported, and perhaps allow slightly longer runs on new housing estates where in the past 2 transformers would have been used but were only just required.
Mike.

AJJewsbury said:

Interesting - I hadn't heard of the recent proposed changes before.

It seems to be very recent - see eFIXX article here. It is not clear whether a consultation has been opened, but since I cannot find one, it is probably still a proposal to consult.

As the article says, the ESQCR would have to be amended first.

AJJewsbury said:

obviously dim lamps or unacceptable reduction in service life

Yes, 220 V lamps were noticeably brighter, but not for long.

It appears that the intention is to drop the target mean voltage (taken over a period) in order to allow for excessive household generation. At one time the grid had to cope with peaks of demand, but now it is peaks of supply.

My rough understanding was that this adjustment to the lower voltage limit was an accommodation of potential effects of prosumer generation/consumption fluctuations at the point of customer supply.

This was so that the DNOs didn't need to change anything on their side, and that if extra customer loading dragged voltages down a bit they wouldn't be forced to make adjustments (or they could make changes if generation was pushing old setting too high).

Meanwhile I saw a YT video about New Zealand also adjusting their high side limit to give headroom on long lines for cases where customer generation made their supply voltage higher than current limits. The newly announced NZ Grid Voltage Increase explained 

New Zealand have not just moved the upper limit, but both, and are going from 230 +/-6% to 230+/- 10% 

According to their energy networks association bulletin

This means that they will be like us there will be no allowance at all between supply spec and product spec for voltage drops within installations.

Mike.