They don’t normally pay part weeks backpay. Normally, the award begins on the Wednesday after you called (so in your case the 12/11/25) and then backpay is paid until the Tuesday on or before the date you are paid the backpay (so in your case the 30/12/25) Any time between that Tuesday and when your receive backpay is accounted for in the normal ongoing payments. That means in your case you should receive 7 weeks backpay.
Besides, it still doesn’t add up even if it is 6 weeks plus some days of HRC/HRM.
6 weeks of HRC/HRM is £187.45 x 6 = £1,124.70.
The daily calculation looks like the following:
The daily rate is £187.45 / 7 = £26.78 (rounded to nearest pence)
1 day is £26.78 x 1 = £26.78
2 days are £26.78 x 2 = £53.56
3 days are £26.78 x 3 = £80.34
4 days are 26.78 x 4 = £107.12
So 6 weeks 3 days is £1,124.70 + £80.34 = £1,205.04
And 6 weeks 4 days is £1,124.70 + £107.12 = £1,231.82
As you can see, they still don’t add up to £1,226.40 before or after accounting for the Christmas bonus.