Hmm! You are indeed lucky if that works for you
Pretty well straight out of CAP 371:
A Commander is authorised to exercise his discretion in the following circumstances and to the limits set.
In a Flying Duty Period involving 2 or more sectors, up to a maximum of 2 hours discretion may be exercised prior to the first and subsequent sectors. This may be up to 3 hours prior to the start of a single sector flight, or immediately prior to the last sector on a multi-sector flight.