These are the restrictions laid down on reasons for leaving the house
- shopping for basic necessities, for example food and medicine, which must be as infrequent as possible
- one form of exercise a day, for example a run, walk, or cycle – alone or with members of your household
- any medical need, or to provide care or to help a vulnerable person
- travelling to and from work, but only where this absolutely cannot be done from home
So the OP can cycle commute as the last point covers it (my bold). Technically I'm classified as a key worker and some aspects of my job can't be done from home, so on the days I do go in, I will be combining points 1, 2 and 4 as I extend the commute for exercise and get any necessary shopping on the way in to or on the way home from work.