Are the taps or the dies engraved HSS - if High Speed Steel this will be a good usable set - if not they are probably only carbon steel - less durable and fairly quick to blunt... The former is used on professional tool for long life and heavy usage, the latter for home /DIY/occasional use... Dormer and Presto were the top two UK makers of taps and dies.
For information, HSS is an alloy steel, containing tungsten first created by Mushet in Sheffield in 1868 (see
http://en.wikipedia.org/wiki/Mushet_steel) - since then its formula has been frequently improved. It is a self hardening steel, that doesn't need quenching, and will continue to cut for a while even when approaching red heat (on a lathe or drill).
(High) carbon steels are those containing 0.8 to 1.2% carbon - they can be hardened, and if not tempered remain very hard, but brittle - for taps and dies they are in this state - so cut well, but soon blunt and will easily break if over-stressed... More recently this quality of tool is made in other (non HSS) alloy steels to improve toughness and wear resistance - they are heat treated to obtain a good balance between hardness, durabilty and toughness.....
