...pendant le congé de maternité".
À mon avis il faut garder KIT days et expliquer par une (longue...mais explicite) périphrase.
Pas trouvé de formule consacrée.

"Working in the MPP for the employer paying you SMP - Keeping in Touch (KIT) days
You can work under your contract of service for the employer paying you SMP for up to 10 days during your MPP without losing any SMP. These special days are known as KIT days.

KIT days are intended to help you keep in touch with your workplace and allow you to do some work during your Maternity Pay Period without affecting your SMP. They could also help ease your eventual return to work. The type of work you do could be attending work for a training course or for an appraisal interview. These are just examples, but whether you take advantage of these days is your choice. Both you and your employer should agree that you can work on those days. Your employer does not have any right to insist that you work.

Any work you do as a KIT day, even as little as half an hour for example, will be counted as a whole day for KIT days. They can be taken as single days; in blocks of two or more days; or can be taken consecutively. Once you have used up your 10 KIT days and you do any further work, you will lose a week’s SMP for the week in the Maternity Pay Period in which you have done that work. If a week in your Maternity Pay Period contains only KIT days, you will be paid SMP for that week. If a week in your Maternity Pay Period contains the last KIT day and you do a further days work in the same week for the employer paying you SMP, you will lose SMP for that week.

http://www.dwp.gov.uk/publications/specialist-guides/technic...