Buckingham first day cover.
This cover has 10 commemorative ‘Olympic and Paralympic Games 2012 stamps issued by Royal Mail on a composite sheet on 27 July 2011.

The stamps in the set and on this cover are:-

1st Slalom
1st Paralympic Games: Table Tennis 
1st Athletics Field
1st Paralympic Games: Archery
1st Modern Pentathlon 
1st Gymnastics 
1st Basketball 
1st Paralympic Games: Rowing 
1st Fencing 
1st Badminton 

This cover is postmarked:-  Sporting Disciplines, London E20, 27.07.11

The cover has the genuine hand signed signature of Paul Goodison 

The reverse of the cover has the certificate of authenticity on a small label attached.
This states:- Only 51 of these Olympic covers which is 1 of a set of 3 featuring 2 se-tennant strips of 5 stamps from the Royal Mail Composite Sheet & postmarked 27/07/11 have been signed by Paul Goodson MBE.

This cover is number 8 of 51

Paul Martin Goodison, MBE (born in 1977, Brinsworth, Rotherham, South Yorkshire) is an English Olympic gold-medal-winning sailor. He won gold medal at the 2008 Beijing Olympic Games in the Laser class. 
He won many gold medals at the World Championships.
These are:-
2009 Halifax, Laser class
2012 Melges 32 class
2014 Melges 20 class
2016 Hayama Moth class
2017 Malcesine Moth class
2018 Bermuda Moth class

There is an information sheet about him enclosed.

The reverse of the cover has information about The Olympic Games.