UK electricity metering for 100kW+ customers has always used half-hourly interval data. Undoubtedly the meters can be programmed for smaller intervals but HH is what's used across the industry for the purposes of understanding demand profiles in sufficient granularity to enable pricing of contracts and trading of power on the markets.
The advent of demand side response services has required much greater granularity of data, but this tends to be dealt with using additional metering.
From a domestic residential perspective, it's very likely that your typical SMETS2 smart meter is more than capable of providing HH data, since this is what's used for Octopus's Agile tariff (
https://octopus.energy/agile/) but whether your incumbent supplier actually does anything with that data will be supplier dependent. Most suppliers offer HH data services (online graphs of consumption etc.) to larger users as part of their contracts but probably aren't set up to offer this to residential customers.
Either way, it won't tackle monitoring of transients and would only capture measurements at HH intervals.