http://en.wikipedia.org/wiki/William_Craigie says he died on September 2, 1957. He was one of the three editors for volume 10 of the OED, part 2, according to the archive.org record at http://www.archive.org/details/oedxbarch.
http://en.wikipedia.org/wiki/Henry_Bradley says he died in 1923.
http://en.wikipedia.org/wiki/Charles_Talbut_Onions says he died in 1965.
Other editors included James Murray (died 1915).
http://www.copyright.cornell.edu/public_domain/ has a table for copyright durations. Among other things, it says:
Before 1923 Conditions: None In the public domain
1923 through 1977 Published in compliance with all US formalities
(i.e., notice, renewal)^11 <#Footnote_11> 95 years after publication
date <#Footnote_10>
1923 through 1977 Published without compliance with US formalities, and
in the public domain in its home country as of 1 January 1996 In the
public domain
1923 through 1977 Solely published abroad, without compliance with US
formalities or republication in the US, and not in the public domain in
its home country as of 1 January 1996 95 years after publication date
<#Footnote_10>
1923 through 1977 Published in the US less than 30 days after
publication abroad Use the US publication chart to determine duration
1923 through 1977 Published in the US more than 30 days after
publication abroad, without compliance with US formailities, and not in
the public domain in its home country as of 1 January 1996 95 years
after publication date <#Footnote_10>
There's a flowchart of copyright in the UK at http://www.museumscopyright.org.uk/private.pdf. The applicable path goes like this:
Is the author known? Yes.
Is the work a literary, dramatic or musical work, a photograph or an engraving, created before 1 August 1989? Yes.
Is the work a photograph taken before 1 June 1957? No.
Was the work published before 1 August 1989? Yes.
Did the author die more than 20 years before publication? If yes, then copyright expires 50 years after first publication; if no, copyright expires 70 years after the death of the author.
http://en.wikipedia.org/wiki/Copyright_law_of_the_United_Kingdom says:
Prior to 1 January 1996, the UK's general copyright term was life
of the author plus 50 years. The extension to life of the author
plus 70 years was introduced by The Duration of Copyright and
Rights in Performances Regulations 1995 (SI 1995/3297); which had
the effect of making EU Council Directive No. 93/98/EEC, created
to harmonise the duration of copyright across the European
Economic Area, law in the UK.
The 1911 copyright act of the UK was the relevant act at the time; I haven't been able to find a copy of it yet.