http://webarchive.nationalarchives.g...ambenefits.pdf
All the info you need is here:
Widow’s or Widower’s
Eligibility
For your widow or widower to
be entitled to receive pension
benefits, the following
conditions apply:
• you must be married at the
time of your death;
• only a legal spouse can
receive a widow’s or
widower’s pension;
• only a decree absolute
ends a marriage and a
widow’s or widower’s
pension entitlement.
(Neither separation nor a
decree nisi is considered
as ending a marriage).