Andrew Gabriel explained :
Not for decades.
Replaced my parents' CU in 1999, and made a call asking for supply
fuse to be resealed. After a couple of years and several meter readers,
it hadn't been done, so I called again. It was still on file, but meter
readers no longer do it, so almost 20 years later (and many meter
readers), it's never been done.

Same here - I broke the seal to do some re-jigging and it was never
sealed until the SM was fitted a couple of years ago. I never requested
it to be resealed after cutting it, it seemed pointless.

In the middle of the broken seal era, we had the cut-out fuse blow and
a distribution engineer round checking a lost supply - neither bothered
to reseal it. SM meter installer did though fit a seal on an isolator
in the meter cupboard, which I had fitted the day before he arrived, I
can't think why he did, because it was downstream of the meter and my
own property.