This is something commonly experienced on the GN route out of King’s Cross, although less common since 2018. You would regularly get southbound Cambridge stopping trains held on the up slow line waiting for a slot on the up fast, at places like Welwyn Garden City, Marshmoor, Potters Bar, New Barnet or Alexandra Palace. It still happens at Hitchin mainly with up Fen Line trains. In these locations you would normally get fairly unrestricted acceleration once clear of the points, though of note is that in those days it was 317/321/365, which didn’t accelerate quite as much as more modern trains (especially 317/321). In my 40 years of using the GN route I’m struggling to think of a time when I’ve been on a train which has been “turned out” onto the up fast line and then had to come to a complete stand at the next signal. I’m sure it will have happened, but certainly very atypical.