I'm not sure why you find 4 in very late March amazing as it's rather normal as a top UV if conditions allow in the South... During low ozone UVs can be high.. 6 and 7s in April kind of high.
At that point (26th) the sun would have reaching the same angle as it will be around 17th of September.
You overlook the fact that the data I've reported is for Reading, not the S Coast, where I am sure you get an earlier edge. As for normal, potentially yes, but in reality no- in fact, it has occurred in only a quarter of years since 2000. By definition, that makes it anomalous rather than normal. If you scroll back through Reading's data, you will see there have only been 5 years since 2000 (20 year period) when 4 has been achieved: 2002, 2003, 2011, the amazing March of 2012, and this year. But the thing is, 2019 is the earliest date during that period when it has been achieved. It has been significantly exceeded in March in 2002- that's amazing for it's extremity. In 2012 there were several 4+ days- that's amazing for its frequency; in 2019 it was achieved on 26th- that's amazing for its earliness. Different reasons for me to be amazed.
As for 7 in April, that was achieved only twice in the same period, in 2000 and 2002, with near misses on two days in 2013. All this again shows the potential, but to call it normal is much further from the mark than calling it amazing.
Bertie, Itchen Valley.
'We'll never see 40 celsius in this country'.