- Caesar Salad
- Call a spade a spade
- Call of the wild
- Camera cannot lie
- Canting Crew
- Can't be overestimated/can't be underestimated
- Can't hold a candle to
- Can't see the wood for the trees
- Canteen culture
- Canterbury pace
- Carbon-copy
- Carbon footprint
- Card-sharp
- Carey Street – On
- Carpe diem
- Carry coals to Newcastle
- Cart before the horse
- Carte blanche
- Cash on the nail
- cast a clout till May be out
- Cast the first stone
- Cat burglar
- Cat got your tongue?
- Cat may look at a king
- Cat out of the bag
- Catbird seat – In the
- Catch a crab
- Cat's Cradle
- Cat's pajamas
- Caught in a cleft stick
- Caught by the short hairs
- Caught red-handed
- Cement overcoat
- Chain is only as strong as its weakest link
- Chaise lounge
- Chalk and cheese
- Champ at the bit
- Chance would be a fine thing
- Change is as good as a rest
- Channel surfing
- Charity begins at home
- Charley horse
- Charm offensive
- Charmed life
- Cheap at half the price
- Cheapskate
- Cheek by jowl
- Cherchez la femme
- Chew the cud
- Chicago overcoat
- Chick flick
- Chickens come home to roost
- Children should be seen and not heard
- Chinese whispers
- Chinless wonder
- Chip off the old block
- Chip on your shoulder
- Chit-chat
- Chock-a-block
- Chop and change
- Chop-chop
- Chow down
- Christmas box
- Christmas card verses
- Clean breast
- Cleanliness is next to godliness
- Clear blue water
- Cleft stick
- Cliff-hanger
- Climb on the bandwagon
- Cloak and dagger
- Clod-hopper
- Clog up
- Close, but no cigar
- Close quarters
- Close your eyes and think of England
- Cloth ears
- Cloud cuckoo land
- Cloud nine
- Club sandwich
- Clue
- Clutch at straws
- Coals to Newcastle
- Coat of many colours
- Cobblers
- Cock-a-hoop
- Cock-sure
- Cock a snook
- Cock and bull story
- Cock-up
- Cockney rhyming slang
- Codswallop
- Cogito ergo sum
- Coin a phrase
- Cold as any stone
- Cold comfort
- Cold enough to freeze the balls off a brass monkey
- Cold feet
- Cold shoulder
- Cold turkey
- Colder than a witch's t**
- Collywobbles
- Colour up
- Come a cropper
- Come clean
- Come on down
- Come to a sticky end
- Come up trumps
- Come what come may
- Comes to the crunch
- on a wing and a prayer
- Common sense
- Comparisons are odious
- Compassion fatigue
- Complete shambles
- Concrete overcoat
- Cook the books
- Cookie cutter
- Cool as a cucumber
- Cool Britannia
- Cop an attitude
- Copper-bottomed
- Cor blimey
- Cordon bleu
- Cost an arm and a leg
- Cotton on to
- Cotton-picking
- Countenance more in sorrow than in anger
- Counting sheep
- Country bumpkin
- Course of true love never did run smooth
- Crack of doom
- Crackpot
- Crapper
- Crinkum-crackum
- Criss-cross
- Crocodile tears
- Crop up
- Crown jewels
- Cry havoc and let slip the dogs of war
- Curate's egg
- Curiosity killed the cat
- Curry favour
- Customer is always right
- Cut and run
- Cut of your jib
- Cut off without a penny
- Cut off your nose to spite your face
- Cut the mustard
- Cut to the chase
- Cute as a bug's ear