Boris Johnson has sparked outrage after pouring milk in a cup of tea before taking the bag out.

The prime minister's hot-drink faux-pas came in an election broadcast on social media.

One viewer wrote on Facebook: "Anyone else annoyed by the fact that he put the milk in whilst the tea bag was still in the mug?"

And then followed a deluge of comments on the etiquette of making the perfect cuppa, with some branding his actions "a sin" and one individual even saying: "Oooo I could never vote for someone who does that."

"I know, bag out before milk in!!!" one person responded.


"Needs to get rid of that filthy habit.....Take the bag out first...." wrote another.

Another viewer added: "Our actual Prime Minister doesn't know how to make a cup of tea. Just how low can we possible (sic) sink?"

However, others leapt to the PM's defence and questioned what all the fuss was about.

"Nope. I always do that!" said one, while another agreed: "It's how we make ours. Scalds the milk."

"My milk goes in before the tea bag, so this was perfectly acceptable to me," added another.

Image: Jane Pettigrew is one of the world's leading tea experts

Jane Pettigrew began her tea career owning a tearoom in the 1980s.

She's now a leading tea expert, and travels the world teaching tea masterclasses, speaking at tea conferences, training staff in tea skills and writing on the many aspects of tea.

Here, she tells Sky News how to make the perfect cup.

When tea companies started to pack their blends inside paper teabags in the 1930s, the allure and charm was lost from the everyday preparation of our favourite brew.

Most people today fill the kettle from the cold tap, set the water to boil, throw a cheap teabag into a mug, submerge it in boiling water, wait 20-30 seconds, fish out the bag, and then drown any flavour they have managed to extract from the leaves with milk and sugar.

To make really good tea, a little more thought and skill is required.

Firstly, treat yourself and buy some good tea. The majority of paper teabags (most of which contain polypropylene plastics) contain very cheap teas that have been blended to make a really low-priced product that delivers colour into the cup but very little true tea flavour.

So pay a little more for biodegradable pyramid teabags (made from corn starch extract) which contain larger particles of tea and therefore deliver a more subtle, interesting, satisfying tea.

Better still, buy loose leaf teas for that wonderful old-fashioned experience of knowing where the tea comes from, of appreciating the colour and appearance of the dry leaves as you scoop them into the pot or mug, and of then drinking a really delicious cuppa.

Image: Brewing time affects the quality of the tea

If you go for loose leaf tea, the easiest way to brew is in a teapot that contains its own infuser basket that can be lifted out when the tea has brewed. Allow 2.5-3g of leaf to approximately 200ml of water.

When it's time to brew, filter your tap water in order to remove all the impurities, such as limescale, chlorine and dissolved heavy metals, that mask the true character of the tea.

Unfiltered water gives the tea a cloudy appearance, causes a scummy layer to develop on the surface of the liquor, and overwhelms the tea's aroma and taste.

Once you've filled the kettle with the filtered water, choose a temperature that suits the tea you're brewing.

Our traditional black teas are best brewed in water at 96˚-98˚C; green teas, so popular now, demand much cooler temperatures, and water at 70˚ -75˚ C will draw out the sweeter notes from the tea, whereas boiling water brews a very bitter tea.

This is because the caffeine and the antioxidants in the leaf have a bitter taste. The trick is to brew long enough to get the goodness and the best flavour from the leaves, but not so long that too much of the caffeine and the antioxidants are released, making the tea taste bitter and unpleasant.

If you're a fan of white teas, brew the beautiful silvery-white leaves at 80˚ for a pale, delicate liquor that reminds you of the colour of a glass of chablis or sauvignon blanc.

Image: To make really good tea, a little more thought and skill is required, says Jane Pettigrew

Temperature-controlled kettles are readily available today and make brewing at a suitable temperature much easier.

Steeping times are also important. Small leaf particles of black tea brew in 1-2 minutes; whole leaf or large leaf black teas need 3-5 minutes.

Most green teas brewed at a lower temperature need from 1.5-3 minutes, and white tea releases its lightly fruity or floral notes when brewed from 3-5 minutes.

When the tea is ready, always separate the wet leaf from the brewed liquor so that the perfect taste cannot change and become too strong, astringent and bitter.

And, whereas a cheap teabag can only be brewed once, some of the world's better-quality loose leaf teas can be brewed 2 or 3 times, giving you great value for money and a wealth of wonderful aromas and flavours.

Most teas drink beautifully on their own without the addition of milk and sugar.

If you want to add milk to stronger black tea and blends, it can go into the cup before or after the tea, depending on your personal preference, but don't add it to the tea while it's brewing in the mug or cup. The addition of milk will cool the temperature of the water and hinder the correct brewing of the tea.

And finally comes the moment you've been working towards - the deeply satisfying pleasure of enjoying your perfectly brewed, wonderful cup of tea.