His father is Prof Donald Eustace Blackwell, Prof of Astronomy at Oxford.
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This birth index might be his as there is a marriage of a Donald E Blackwell to a Nora L Carlton in Howden Yorks in Q1 of 1951 and Cambridge sounds a good place for a future Astronomy Prof at Oxford:

First name(s) CHRISTOPHER J
Last name BLACKWELL
Birth year 1959
Birth quarter 2
Registration month -
Mother's last name CARLTON
District CAMBRIDGE
County Cambridgeshire
Country England
Volume 4A
Page 475
Record set England & Wales births 1837-2006
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Their marriage index from Scotland’s People:

                                                     City    
Year   Surname  Forename Surname  Forename  District    County/     GROS
          (M)   (M)      (F)      (F)                   MR        Data

1996  BLACKWELL CHRISTOPHER JOH GRANT CATRIONA CHARMI  HADDINGTON  /EAST LOTHIAN  722/00 0048
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