Good Morning Britain's resident doctor explained how the government decides which parts of England will go in which tier.
Later today, Health Secretary Matt Hancock will reveal details of its stricter new regional restrictions.
Most of England is expected to be placed in either Tier 2 or 3 when the national lockdown ends next Wednesday.
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Speaking ahead of his speech, Dr Hilary told Susanna Reid and Ben Shephard what factors will be taken into account when deciding the tiers.
They include; infection rate and how many people have tested positive.
Dr Hilary said: "We know there are many places in the country with high prevalence rates and I think when we hear what areas will be in Tier 1, 2 and 3 we can look at that and say 'why are we in Tier 3, 2...'
"It's going to be based on several things, it's going to be based on the amount of infection in your area, whether the NHS in your area has the capacity and whether it's coping, it will be based on whether the infection rate is rising or falling and the percentage of those people who test positive.
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"So almost all those factors will be put into an algorithm and decisions will be made with local authorities to which tier you're in.
"It does make sense because if your local area has got lots and lots of infection, you need to take extra precautions."
