No.1 actions were considered safe only to the 303 Britishicon pressure loadings therefor it was not recommended to be converted to the Epps. The No.4 handles loads comparable to 308Win, while the No3 handles hotter loads that are considered by most dangerous in a No.4. Why? Because the action, just like the Remington M700, can handle running ammunition that is pushing the 60,000PSI range, just like lets say the new Winchester Short (and Super Short) Magnums or the Remington Ultra Mags do.
Are you serious? Max allowable pressure for .308 Winchester is higher than 60,000 PSI, that doesn't mean there are that many manufacturers who would knowningly load it to those pressures but theres a possibility of an owner buying ammo that passes the SAAMI specs and generates such pressures.

The British didn't consider MkVIIIZ safe for use in the No.4 except in emergency situations when other ammo was in short supply, and MkVIIIZ has a working pressure comparable to the max allowable SAAMI standard for .303 which is far lower than the max alowable for the .308.
If the low end of the 7.62 pressures already exceed max allowable for the 303 then how much safety margin would you have with max pressure .308 rounds that exceed max .303 pressures by more than 20%?

Since Villers refered to Laidlers statement on the rear sight pin I would naturally figure he meant his pin was damaged in the same way, the locking pin bent and sometimes sheared through by the receiver spreading.
I've seen more than a few No.4 actions with loose fit between the bolt and rear receiver and a gap between the rear sight mountings and the sight, and with bent locking pins, I'd always figured that for loose wartime tolerances, but Laidlers article makes it much more likely that these suffered damage from MkVIIIZ ammunition.

If Villiers No.5 is not subjected to 308 ammunition loaded to the highest pressure levels there may never be a problem with it, but if he used max .308 loads for thousands of shots there very well might be damage to rifle even under the best of conditions much less under wartime conditions.

If .308 loads that do not greatly exceed max pressures allowed for the .303 are used then ability to handle those loads is no indicator that the rifle would be safe with max .308 loads.

Such a conversion holds no attraction for me. Though I'd know that it was not suitable for max loads the rifle might end up in the hands of one of my family years after I'm gone and in much worse condition than now, if max pressure .308 or old 7.62 LMG ammo not marked as such was all that was available then it would be an accident in the making.

Now I ask again , would any here load .303 ammunition to 62,000 PSI and sell it as safe for use in No.4 rifles?