The older concept of training out of programme (OOP) has now been refined, and categorised, by Health Education England (HEE). Only OOPT (T for training), or OOPR (R for research), to an accredited centre will not have an impact on your Completed Certificate of Training (CCT). Most experience in the developing world, the categories OOPE (experience), OOPC (career break), will not count towards your training time despite its significant value to you as an individual.
The HEE PGMDE site has useful FAQs about when, how and where to apply for your OOP
Be aware of what visits are coming up and plan well ahead with your Educational Supervisor, where you are or would be working, and the Training Programme Director (TPD) in your region. The COPMED Gold Guide 2020 OOP form is a useful thing to have for your discussion with them:
OOP Form will need to be signed off by the Postgraduate Dean responsible for your training programme, before you can take significant time out.