British casual slang terms for different items, concepts and situations that we actually use in daily life!

British Slang:)

£5, £10 (Either the value or the physical note)
Ex. "You can get cocktails for a tenner in happy hour"

Extremely tired (having done a lot)
Ex. "Work was so busy today, i'm knackered"

To steal (pickpocket) from someone on the street
Ex. "there has been someone trying to mug people, be careful"

Proud of oneself
Ex. "Nice! I got an A! I'm pretty chuffed with that"

Used to show agreement, to make a point or as an equivalent to 'of course'. Short form of "Isn't it?"
Ex. "Are you coming with us to town?" "I still have work innit"

used after adjectives or by itself to mean 'about' 'sort of' or 'approximately'
Ex. "Are you busy?" "ish. I just have a few more documents to read then I'll be done"

A lot of 
Ex. "I can't come tomorrow I've got bare work to do for Monday"

uncomfortably humid
Ex. "It wasn't the hottest day ever, but it was really muggy"

slight insult. A person who has done something embarrassing or shameful.
Ex. "that was very muggy of him"

Big and muscular. Typically refers to people but can also be used to refer to big items in general.
Ex. "He started going to the gym last year so he's pretty hench now"

Really disappointed, sad about something (sometimes on someone else's behalf)
Ex. "He couldn't go to the show in the end because of work. I'm gutted for him, he was so excited"

Broke, completely poor, no money
Ex. "I'll go broke if I keep buying so many shoes"

To succeed romantically with someone. Usually in a casual way.

Rich, wealthy
Ex. "Whoever lives in that house must be minted"

Badly completed task/ something that has gone wrong
Ex. "That bathroom is a complete botch job. We need to renovate the whole thing"

Money
Ex. "She has a lot of dosh to spend"

Spend a lot of money and/or effort on something
Ex. "Jemma really splashed out for the party"

Strong cup of tea, normally with only a very small amount of sugar and milk.