The most completely systematised of all the main line services is that of the Worcester line. Departures from Paddington are at exact 2hr intervals from 9.15 a.m. to 7.15 p.m., and in the up direction from Worcester at similar intervals from 9.10 a.m. to 7.10 p.m., with the 7.25 a.m. up in addition.
Source: wiktionary