Hi Spotter
First obvious difference is the fuze adapter, which is the standard US pattern. Secondly, the shape of the machining on the top end is slightly different to the British pattern. Thirdly, early US pull Switches that predate the more common US M1 pattern are machined out of brass, and finished with an olive green paint rather than the usual MD1 blackened finish which you are familiar with. Fourthly, these switches were often supplied with a fixing loop made out of braided steel wire that is soldered to the body, rather than the usual MD1 L shaped bracket. Looks improvised, but that is how they were made. Finally, MD1 Switches are normally marked MD1, with an A number denoting the individual inspector, stamped on the collar.
Picture 1 is definitely a US model, and I would suggest that picture 2 may be British manufactured models - bad to tell without being able to see the adaptor.
I think that these early US pull switches were made to UK specifications to supplement our supplies, and that they became obsolete with the adoption of the standard M1 pull switch. I will try to find some pictures tomorrow to illustrate. Bonnex can probably add some more detail!
Hope this helps.
Cheers
Switch