How To Speak Posh English
If you listen to the Queen speak, you'd never find that she rushes through her speech. Her tempo is not even medium, let alone rapid. Posh English is spoken slightly slower than the medium pace. This is because it requires that your diction is clear and you elongate the vowel sounds.
For "lovely", try saying "laah-v-lay".
Practice listening to yourself while you speak. Keep in mind that each word you say is clear and "heavy". Ross from the TV show Friends is a classic example of someone who speaks posh English.
That posh people are monotonous is definitely a myth. If anything, people who speak posh English always look to create a dramatic effect with what they have to say. In other words, their tone reflects clearly whether they are angry, sad, dull, disappointed, excited, delighted and so on.
Make sure when you say, for example, "okay", or "alright", people are able to tell whether it's a happy "alright" or a displeased "alright".
The vocabulary of a person who speaks posh English extends up to over 30,000 words. This implies they read extensively. Your vocabulary must be broad-ranging if you want to speak the Queen's English.
Avoid vague terms like "nice". Say "marvellous", or "glorious", or "splendid".
Also, use "indeed" a lot. "Indeed, I do think they have managed it in spectacular fashion."
LANGUAGE AND GRAMMAR
Posh English is characterised by flawless grammar and sentence formation.
Avoid using contractions. Instead of saying "I've no idea whatsoever", say "I have no idea whatsoever".
Adding an unnecessary "do" before the verb (ex. "I do see my hat by the rack") is generally used by the English upper class. This does indeed, I believe, create a studied-at-Eton effect.