Use By dates on meat are for "use" - cooking, freezing.
So once cooked, they have extended life, so you do not need to consume the whole product on the day of the RAW use by date.
This is really only applicable to chicken/poultry and fish, as red meat keeps MUCH longer than the Use By dates they use and actually get better with age (this is why you don't by the reddest meat at the butchers, but the darkest).
If your chicken is use by 1.1.10, you cook it on this date (or freeze it) you can then consume it within 3 days (if the leftovers have been refridgerated.) You can also freeze the cooked meat and it will last for about 1-3 months in the freezer depending on what it is.