Instrument approach tolerances are recommended in ICAO PANS-OPS, and are specified for each country in their respective AIP.
http://www.pprune.org/tech-log/76882...tolerance.html
http://www.pprune.org/tech-log/22428...s-dme-arc.html
The UK-AIP is silent on the matter of DME arcs, and only specifies tolerances for ILS, VOR and NDB tracking:
UK AIP ENR 1.5 — HOLDING, APPROACH AND DEPARTURE PROCEDURES
3.15 Established
3.15.1 Aircraft are considered to be 'established' when they are within half full scale deflection for the ILS and VOR, or within ± 5°
of the required bearing for NDB(L).
... compared to the
Australian AIP ENR, which states:
1.20.2 ... "Established" means being within half full scale deflection for the ILS, VOR and GPS, within ±5º of the required bearing for the NDB, or within ±2NM of the DME arc.