There is much needed clarity for how current restrictions affect our birding on the "bbc news (UK)" website. Look at the item headed "Police fine people over social distancing". There it is reported that the head of the National Police Chiefs Council says that exercise more than once a day is NOT banned. The key requirement is to avoid going close to someone who is not a household member.
There is a link to the complete wording of the emergency legislation that was passed yesterday. This has a list of justifiable reasons for leaving home. One of these is for the purpose of exercise - with nothing said about how many times a day we can exercise.
If you have a dog and no garden, it would amount to cruelty only to take it out once a day.
Good birding, Pete