They could be operated by either locomotives push/pull or EMUs.
The Waterloo - Poole trains used them (2 x 4-TC + 1 x 4-REP high powered EMU). The 4-REP was at the London end pushing the train to Bournemouth where it was uncoupled and a class 33 attached at the front to pull it the rest of the way.
The class 33 then pushed the two 4-TCs back to Bournemout where it was uncoupled. A 4-REP was couplued to the front which then pulled the train back to Waterloo.