Lateral flow tests have become a part of every day life for many.

They are a major defence against the spread of Covid, and the Government has urged us all to test regularly.

But what are the rules around taking a test? Here’s everything you need to know.

No, but only for a short time.

The NHS recommends that you do not eat or drink for at least 30 minutes before doing the test to reduce the risk of spoiling the test.

Professor Azeem Majeed, head of primary care and public health at Imperial College London, said “correct technique… has a big affect on the result. Make sure you don’t eat for a little while beforehand, make sure you blow your nose and wash your hands”.

The reason behind these rules is to ensure a “clean sample”, he added. “If you’ve still got food [residue] in your mouth, you could just coat the swab with that and that could affect the result. You could also pick up a bit of snot, and that might obscure the result.”

He added: “I also advise swabbing the throat as well as the nose [despite LFT kit instructions to only swab your nose], on the grounds that if you swab from more sites you’re more likely to pick up infection than by swabbing the nose only.”

To increase the chances of a more accurate result, swab for at least 10 seconds on both tonsils, and then in each nostril, while “turning the swab around”, the professor suggests.

Lateral flow devices are small white rectangles made of plastic with a testing strip inside.

There is a small well at the bottom of the device with the letter “S” next to it. This is where you drop your sample.

Above this there is a window to the testing strip. Towards the top of the window is the letter “C”, and below it is the letter “T”.

The C stands for “control” and the T stands for “test”.

Once you have dropped your sample into the well, a red line should appear next to the C relatively quickly. This line should be present every time you do a lateral flow test.

If a red line appears next to the T that means you have tested positive. If there is no line, that means you have tested negative.

Even if the line next to the T is extremely faint, that still means your test is positive.

Government guidance states: “Result lines may appear smudged or faint, but they are still valid results and must be reported.”

However, you should be careful to read the instructions for your lateral flow tests before taking them, as sometimes they can show false positives if you read them too late.

The instructions will tell you how long to wait before checking your test. Most say between 15-30 minutes.

NHS A&E doctor Nathan Hudson-Peacock has said a second line which appears after the 30-minute window may not indicate a positive result.

To take an antigen test, you take a swab from inside your nostril, the back of your throat, or both, depending on the specific test you are using.

You then mix that swab with solution and drip it onto a device which contains a test strip.

The test strip has antibodies specific to the Covid-19 virus painted on it in a thin line.

These antibodies will bind to any antigen in the sample. If the testing strip detects the virus, it will show up as a thin red line next to the T on the device.

You can order a packet of NHS tests for free from the Government here. These cannot be used for travel.

You can also pick up up to two packs of seven up at a pharmacy – this link will show you where to get the tests near you.

Some test sites still offer home tests for collection – you can find where here.

If you attend or work at a school, college or nursery you can get rapid tests through them.

If you are travelling you must buy a lateral flow test from a private company.

You must report your result every time you do a lateral flow at home or at work, even if the result is negative.

You need to report your result within 24 hours of getting it.

This helps scientists track the spread of Covid-19 and spot new outbreaks faster.

You can report the result on gov.uk.

If you cannot use the online service, call 119 (free for mobiles and landlines). Lines are open every day, 7am to 11pm, and 119 provides support in 200 languages.

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