1. Au fait – this is an example of a French expression that has become part of the English Language. It means to have good detailed knowledge of something. (This is not slang but a very British English expression.)
2. Blinding – if something is blinding, it means that it’s excellent.
3. Bugger all – if you’ve got bugger all for dinner, it means you have nothing. (This is an impolite expression so use it with caution)
4. Cock up – This can be used as a verb or a noun and it means to make a serious mistake or a mistake. (It has nothing to do with male parts!)
5. Donkeys’ years – a long time or ages
6. Gobsmacked - “Gob” is mouth in British English and if you smack it, you probably would do it because you are amazed or shocked.
7. Gormless – another way to say vacant or clueless.
8. Gutted – really upset.
9. Hunky-dory – fine, going well
10. Knackered – very tired, exhausted
11. Lurgy – if you’ve got the lurgy, it means you are ill with the flu or other mild disease.
12. Nice one! – If someone is impressed by what you’ve done, they could use this expression. It’s similar to “good job” in American English. It can also be used sarcastically.