They are saying twenty quid, which is slang for 20 pounds sterling (the currency called GBP). It's worth about 30 bucks (USD).
A 'doddle' in British slang means something is easy. For example: 'that essay was a doddle!'.
'Let's gave a do' is a British expression meaning 'let's have a party!' For example: 'You're engaged? Let's have a do to celebrate!'
'C of E' stands for the Church of England, which is the established Christian church in England. When a British person refers to 'C of E,' they are typically talking about this church or someone affiliated with it.
Bladdered is one of the many British slang words that means 'drunk'. For example: 'Look at Jake, he's absolutely bladdered!'
'Brassed off' is British slang meaning 'fed up'. For example: 'I am really brassed off with all this homework!'
If someone says that they validate you as a person, they mean that they consider you to be a worthwhile person.
Quit talking, listen to what she says. YOU DO NOT HAVE TO AGREE, but a person can not argue by themsleves
Usually to "quit somebody" means to give up on them. So, when someone says they "quit you", that means they are done trying to help you or convince you of something.
You mean 'C of E'. This is commonly used to refer to the Church of England. For example: 'The C of E is bankrupt again'.
When a British person says 'Best of British to you,' it is a phrase used to wish someone good luck or success. It is similar to saying 'Good luck' or 'All the best.' It is derived from the British phrase 'Best of British luck,' which is commonly used to encourage and support someone.
This probably isn't what you think it is. A cock up in British slang means 'a mistake'. For example: 'I made a total cock up of that pie!'
'That's beastly' in British slang means something or someone is nasty or unpleasant. For example: 'Shaun is a rather beastly fellow!' or 'that smells incredibly beastly!'