Wonderful British Food -
Cheddar cheese
Branston pickle
Cream Teas
Battenburg
Marmite
Mr Whippy
Hot Cross Buns
Foodstuffs with crazy names - Toad in the hole, Bubble and Squeak, Spotted Dick
Cornish Pasties
British strawberries in the early summer
Bacon sandwiches
Rich tea biscuits
Salt and vinegar crisps
Tea, Tea, Tea (never the same abroad and I always take a large bag of teabags when I travel)
Conversely our ability to embrace food from all over the world and be willing to try things we are unfamiliar with.
Punting in Oxford on a summer's day (whilst imagining you are a character in Brideshead Revisited)
Dry stone walls and narrow country lanes
Villages with wonderful names eg Cold Christmas, Skinners Bottom
The first daffodils poking through
Beautiful old buildings standing shoulder to shoulder with modern ones
Wind in the Willows
Alice in Wonderland
Swallows and Amazons
Malory Towers
Winnie the Pooh
Jane Austen
The Bronte sisters
Charles Dickens
George Eliot
Folk Music from every part of the UK
Elgar's Nimrod
Festivals that are individual to particular regions or villages
Summer Fetes
Charity Shops
Shetland ponies
Hedgehogs
Dogs being treated like part of the family
Our ability to enter competitions when we are well aware we have no hope in hell of winning eg Eddie the Eagle, Eurovision, the World Cup 
Radio 4
Gardeners World
Glastonbury
Wimbledon
National Trust
BBC
Carry on Films (yes I know they are very un PC but they evoke so many childhood memories and still make me laugh 
Not showing too much emotion in public (unless completely pissed and then overemoting to strangers)
Sitting in the garden on a summer's day and asking whether the sun is over the yard arm
Cricket and the fact that they stop for tea!
The Queen who must have the best poker face in the world as you never know quite what she's thinking.
Obsession with the weather, and ability to be pessimistic even when it's nice (looking at you DM - "well it won't last ..." 