Looking into this further I've found that the /usr/share/zoneinfo/Europe/London file varies between machines.

Doing zdump -v /usr/share/zoneinfo/Europe/London on the incorrect GMT machines gives:

London Fri Dec 13 20:45:52 1901 UTC = Fri Dec 13 20:45:52 1901 London isdst=0 gmtoff=0

London Sat Dec 14 20:45:52 1901 UTC = Sat Dec 14 20:45:52 1901 London isdst=0 gmtoff=0

London Mon Jan 18 03:14:07 2038 UTC = Mon Jan 18 03:14:07 2038 London isdst=0 gmtoff=0

London Tue Jan 19 03:14:07 2038 UTC = Tue Jan 19 03:14:07 2038 London isdst=0 gmtoff=0

Whereas on the correct BST machines it has hundreds of lines detailing the daylight saving changes every year up to 2038.

Any idea how I can recreate this file correctly?