Bob Van Arsdell writes:

Three legendary forgers, Giovanni Cavino, Carl Becker and Constantine Christodoulos, are renowned for producing extremely deceptive fakes. Their coins occasionally appear on the market undetected, showing they can still fool the experts. The lives and careers of these forgers have already been published. This article compares their work to that of a troublesome forger of Ancient British coins.

The Haslemere Forger began faking Celtic coins around June 1960 and never stopped

By 1991, he was producing some superb forgeries, ones that fooled almost everyone at the time. By comparing his 1991 Cheriton stater to the work of the legendary forgers of the past, we can appreciate how good (and how dangerous) his fakes are.

Christodoulos struck fakes from 1900 to 1914

Becker produced fakes during the 1820s

Giovanni Cavino lived from 1500 to 1570 and was active in the mid 1500s

Not only was Cavino an accomplished die cutter, but he also was expert at antiquing and patinating his coins. This Ostia sestertius shows convincing wear and has a beautiful brown and green patina.

Summary
The Haslemere Forger had improved his work greatly from 1960 to 1991. At the end of that period, he was capable of work rivaling that of Constantine Christodoulos. If he continued to improve his work after that time, he may very well have been capable of forgeries as good as Becker or Cavino.

The Haslemere Forger is certainly in the league of the legendary forgers. As such, he should be seen as a dangerous falsifier of the archaeological and numismatic records.

To read the complete article, see:
Modern Celtic Fakes 5 - Haslemere vs. the legendary forgers(vanarsdellcelticcoinageofbritain.com/coin_articles/v2014e.html)