The English Chess Federation did not switch to the international standard Elo rating system until 2020.
In July 2020 the English Chess Federation moved to publishing ratings monthly using a modified Elo system.
The more games played, the more the end-of-cycle re-grading is affected directly or indirectly by this tiny inflationary effect at the bottom of the league so ECF grades are nonzero-sum.
Countering this, a retiring or deceased master who had not appreciably shed points loses their accumulation available, otherwise open to competitors.
The Federation has to recalibrate grades based on this discrete variable, and looks at the very approximate other-systems conversion formulae in so doing.
Grades far above 200 lose much of their significance as very strong players tend to play mostly in internationally rated tournaments.
The 150 Attack, a no-nonsense response to the Pirc Defence popularised by British players, derives from this system.
Per Sam Collins in Understanding the Chess Openings this is because "even a 150-rated player could handle the White side".
Due to the inherent simplicity, a benefits it has over the Elo rating system used by FIDE, is scores are simple after each result without coded software or a calculator, and retention of personal grades over a cycle of typically at least 30 games.
It is often used by organisers of English congresses to determine qualification for grade-restricted events when a player has an Elo rating only.