Her birth index:

First name(s) MARY
Last name MELLON
Birth year 1921
Birth quarter 2
Mother's maiden name Keenan
District Stockton
County Durham
Country England
Volume 10A
Page 229/6047/S
Record set England & Wales Births 1837-2006
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The following Boynton children were born to a Mellon mother between 1952 and 1972:

Last Name First Name Born Died Event   Location

Boynton Anthony 1954 — 1954 Middlesbrough, Yorkshire
Boynton Laurance P 1955 — 1955 Middlesbrough, Yorkshire
Boynton Gerard 1956 — 1956 Middlesbrough, Yorkshire
Boynton James 1956 — 1956 Middlesbrough, Yorkshire
Boynton Bernard 1958 — 1958 Middlesbrough, Yorkshire
Boynton Mary B 1958 — 1958 Middlesbrough, Yorkshire

This looks like there were two pairs of twins in 1956 and 1958, confirmed by the registration quarters being the same.  Though there could be a second Boynton family with a Mellon mother.
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Mary’s death index:

First name(s) MARY
Last name BOYNTON
Gender Female
Birth day 21
Birth month 5
Birth year 1921
Death quarter 4
Death year 1999
District Stockton
District number 3501A
Register number A6
Entry number 158
Date of registration mm/yy 1099
County Durham
Country England
Record set England & Wales Deaths 1837-2007
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Their marriage index:

First name(s) MARY
Last name MELLON
Marriage quarter 3
Marriage year 1953
MARY MELLON married one of these people
Laurance Boynton
Spouse's last name Boynton
District Durham South Eastern
County Durham
Country England
Volume 1A
Page number 1810
Record set England & Wales Marriages 1837-2005
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Thanks to Laurence Philip Boynton for the actual date and place of the marriage.
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