It's a shambles (as per usual) that they announce it without telling us which areas. I would have hoped it was at least all Tier 4 areas but they said it was only the worst areas.
A total guess but I reckon it'll be those reported as being worst hit, yesterday, i.e.:
"Of the 315 local areas in England, 238 (76%) have seen a rise in case rates, 75 (24%) have seen a fall, and two are unchanged."
Brentwood, Tier 4, 1258.1, (969), 1134.8, (874)
Epping Forest, Tier 4, 1256.0, (1654), 1179.3, (1553)
Thurrock, Tier 4, 1181.6, (2060), 1295.2, (2258)
Havering, Tier 4, 1068.8, (2774), 1222.5, (3173)
Castle Point, Tier 4, 1047.8, (947), 1036.8, (937)
Broxbourne, Tier 4, 1037.2, (1009), 841.9, (819)
Redbridge, Tier 4, 1008.4, (3078), 1083.5, (3307)
Bexley, Tier 4, 987.2, (2451), 868.3, (2156)
Basildon, Tier 4, 954.6, (1787), 1121.8, (2100)
Harlow, Tier 4, 933.8, (813), 737.4, (642)
Barking and Dagenham, Tier 4, 932.3, (1985), 997.2, (2123)
Southend-on-Sea, Tier 4, 931.1, (1705), 943.1, (1727)
Rochford, Tier 4, 929.4, (812), 1061.0, (927)
Enfield, Tier 4, 929.3, (3102), 818.8, (2733)
Hastings, Tier 4, 917.3, (850), 958.3, (888)
Tower Hamlets, Tier 4, 892.4, (2898), 822.2, (2670)
Newham, Tier 4, 880.7, (3110), 798.3, (2819)
Hertsmere, Tier 4, 864.5, (907), 598.6, (628)
Dartford, Tier 4, 849.0, (956), 805.5, (907)
Medway, Tier 4, 847.6, (2361), 1078.1, (3003)
"The data includes (from left to right), the rate of new cases and the number (in brackets) of new cases recorded in the seven days to December 25 and the rate of new cases and the number (in brackets) of new cases in the seven days to December 18."
"The rate is expressed as the number of new cases per 100,000 people. Data for the most recent four days (December 26-29) has been excluded as it is incomplete and does not reflect the true number of cases."
uk.news.yahoo.com/tougher-tier-4-covid-restrictions-worst-hit-areas-165106819.html