Faculty Office Marriage Licence Allegations (1701-1850) 
from English Origins the original can be ordered at 10 pounds

22 Dec 1800 MARGETTS John (Doctor) LANKSHEAR Mary

daughter of 1767 Joseph LANKSHEAR marriage Elizabeth SYLVESTER

But see 1792 Mary Lankshear marriage William Perkins at St. Andrew Holborn - perhaps  Mary born 1773 ? - it could be the other Mary married Dr Margetts - I am not fully satisfied on which was which
Except this 1768 Mary has a sister called Harriett who might be a connection with
1823 HARRIET LANKSHEAR in Tasmania marriage to HORATIO WILLIAM MASON not the same woman as Tasmanian girl is too young 

----- John Margetts 

This one was proposed but must be wrong

JOHN MARGETTS 
Birth: 
Christening: 30 MAR 1771 Theddingworth, Leicester, England 
Death: 21 APR 1771 
Father: PECK MARGETTS Family 
Mother: FRANCES 
Extracted birth or christening record C059891 1738 - 1872

This guy looks more likely

JOHN MARGETTS 
Birth: 
Christening: 27 AUG 1780 Brize Norton, Oxford, England 
Father: BENJAMIN MARGETTS Family 
Mother: MARY 
But maybe the 1779 second son is better

JOHN MARGETTS 

Birth: 
Christening: 01 AUG 1779 Theddingworth, Leicester, England 

Parents: 
Father: PECK MARGETTS 
Mother: FRANCES